Dictionary of the History of Ideas Studies of Selected Pivotal Ideas |
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![]() | Dictionary of the History of Ideas | ![]() |
CERTAINTY IN SEVENTEENTH-
CENTURY
THOUGHT
The problem of the certainty of knowledge was not
new in the seventeenth century. In the preceding cen-
tury the Reformation brought to the fore the question
of the
reliability of religious knowledge, particularly
the question of which
church—Catholic or Protestant—
could provide the best
guarantee of the truth of its
doctrines. The revival of learning in the
Renaissance
brought to the attention of the learned of the time
the
writings of the ancient Greek skeptics, particularly
of Sextus Empiricus
(ca. A.D. 200). Most deeply affected
by this discovery was Michel de
Montaigne who in
his Apology for Raymond Sebond
extended the argu-
ments of the skeptics to
raise questions about the relia-
bility of
all our knowledge. The issue involved in the
resurgence of skepticism was
the question of how cer-
tain one can be of what
he believes. The skeptic claims
one can have no knowledge at all; at best one must
remain in
doubt and suspend judgment. If the structure
of nature is complex, if the
senses sometimes deceive,
if one's thought processes do not match the
structure
of nature, then nothing is certain. Montaigne asks: If
the
senses cannot be trusted how reliable is scientific
knowledge? If reason
errs how reliable are claims to
know of God's existence and nature? If
moral principles
cannot be justified then how seriously ought one to
pursue the good life or try to do what is right?
If the problem of certainty was not new for the
seventeenth century, the
solutions to it were. In addi-
tion to the
suspension of judgment counselled by such
skeptics as François de
La Mothe Le Vayer, Pierre
Charron, and François Veron, two
alternative views
were developed. First there was the extreme opposite
view, that of dogmatism. Francis Bacon argued that
by furnishing the senses
with mechanical aids and the
mind with a new method of inquiry one can
gain
certain knowledge about nature. René Descartes ar-
gued that by grounding all knowledge on clear
and
distinct ideas of the self and of God, completely certain
knowledge can be gained about self, God, and the
world. The second major
alternative to skepticism was
the claim that a middle way could be found
between
the extremes of skeptical uncertainty and complete
certainty,
thereby forming a perspective which later
became the foundation of what we
now call the “sci-
entific” temperament. This view has been called
“con-
structive
skepticism.” On the Continent this view was
initially worked out
in the context of science by Marin
Mersenne and Pierre Gassendi. In England
it was for-
mulated in the context of
theology by a liberal Angli-
can, a convert
from Catholicism, William Chilling-
worth,
and later systematized and applied to the theory
of science by such early
members of the Royal Society
of London as John Wilkins and Joseph Glanvill.
It was
applied in the sciences by such men as Robert Boyle
and Sir
Isaac Newton. Finally, it received its definitive
expression in the
philosophical writings of John Locke.
However, it was not completely
assimilated into the
mainstream of European thought until the
dogmatism
of Descartes was dealt its final blow by David Hume.
Francis Bacon, the reputed father of modern experi-
mental science, was one of the first to formulate a way
out of
the skeptical crisis. Though his emphasis upon
experimental procedures and
on the utility of science
for the benefit of human life won him acclaim in
his
own century, it was not his views on the certainty of
the results
of scientific inquiry that were the decisive
ones in the shaping of the
views of early members of
the Royal Society and of the scientific
temperament.
The best known and perhaps most serious attempt
to solve the skeptical
crisis of the seventeenth century
the Reformation, the new developments in science, and
the resurgence of skepticism had thrown all accepted
claims to knowledge into question. He was personally
acquainted with such skeptics as Mersenne and Veron
and knew the arguments of Montaigne and Charron.
The view he found among his immediate acquaintances
was that everything was subject to doubt. Probability
was the most that could be claimed for anything.
Descartes realized that if there are only probabilities,
then there is no secure foundation for truth; for then
there is no adequate criterion by which to distinguish
truth from falsity. The strategy of his position is to
follow the arguments of the skeptics to their conclu-
sion, to reject everything as false, and in the depths
of uncertainty to find truth and a criterion of truth.
This criterion is then tied to the goodness of God.
In the Discourse on Method (1637) Descartes had
formulated a “natural method” to assure certainty in
the sciences. The first rule of this method was “...
to accept
nothing as true which I did not clearly rec-
ognize to be so... to accept... nothing more than
what was presented
to my mind so clearly and dis-
tinctly that I
could have no occasion to doubt it.” Ten
years before publishing
the Meditations (1641) he came
to realize that all
knowledge was under attack and
therefore the criterion would have to be
applied more
extensively. Indeed, it became a very definition of
knowledge: to know is to apprehend without any pos-
sibility of error. The Meditations begins with
a re-
hearsal of basic skeptical arguments
from the fallibility
of the senses and problems about being awake or
asleep. In rehearsing such arguments he is claiming
nothing particularly
new; these were the standard
weapons of the skeptics. To accept them was to
admit
that the senses were unreliable sources of knowledge
of the
nature of the external world. Descartes realized
that to overcome
skepticism he had to go all the way.
Hence he formulates an argument more
critical than
any presented by any preceding skeptic: the argument
based on the possibility that there is an evil demon
whose sole business is
to make us believe true what
may in fact be false. Unless this serious
doubt is over-
come, skepticism will always
triumph, for there is then
no dependable criterion of truth. Unless one can
ex-
orcise the evil demon no criterion is
possible; what
appears as self-evident may in fact be false. Even such
simple matters as that a square has four sides or that
three plus two is
equal to five may be erroneous. Given
the possibility of the evil demon all
evidence and the
rational processes of interpreting it are subject to
error.
Hence what can be known? Descartes suggests that
his use of
skeptical arguments differs from that of the
skeptics' use of them. Whereas
they used them to show
that nothing can be known he is using them to show
precisely
that truth and a criterion for its discovery
can be found. Descartes finds
the answer to doubt in
the famous cogito ergo
sum (“I think, therefore I am”).
In
formulating the most critical of the arguments of
skepticism one discovers
something true, his own exist-
ence. This
follows not as the conclusion of an argument
but as the conclusion of a
doubt.
Having found this one truth Descartes has also found
the criterion by which
to distinguish truth from falsity:
whatever is as clearly and distinctly
perceived as the
cogito is true. This criterion enables him by the
light
of natural reason to recognize the truth of several
causal
principles with which, in conjunction with the
idea of a perfect being, he
can demonstrate the exist-
ence of a perfect
being, God. This being serves two
functions: first, being perfect he would
not allow man
always to be deceived, thus exorcising the evil demon;
and secondly, he guarantees the correctness of the
criterion. In short, the
criterion is rooted in the good-
ness of God.
From this point Descartes proceeds to
establish the reliability of the
senses and prove the
existence of the physical world. On this
metaphysics
of self, God, and matter, together with the criterion
of
clarity and distinctness, he then rebuilds the scien-
tific description of the world around us. What we
find
in Descartes, then, is the recognition that “The Refor-
mation, the revolution in science, and
the onslaught
of scepticism had crumbled the old foundations that
used
to support the entire framework of man's intel-
lectual achievements. A new age required a new foun-
dation to justify and guarantee what it had
discovered.
Descartes, in the tradition of the great medieval minds,
sought to provide this basis by securing the superstruc-
ture, man's natural knowledge, to the strongest
possible
foundation, the all-powerful, eternal God” (Popkin,
p.
179).
By Descartes' criterion—not to accept anything as
true unless it
is clearly and distinctly perceived—not
only is one subjectively
certain that something is true,
but he is certain that it actually is so.
Without the
goodness of God there is always room for doubt. In
working
out this solution to the skeptical problem
Descartes has offered, as Popkin
argues, a Reformation
solution to an epistemological problem concerning
our
secular knowledge. The Reformers and their opponents
had shown
each other that their views were without
rational justification. The
Reformers, particularly the
Calvinists, had then argued that by a direct
insight they
were privileged to see true principles of faith and by
an
act of divine grace to see that these principles agree
with the rule of
faith, the Scriptures. What Descartes
offers is the same kind of argument
for all, not merely
theological, knowledge. We perceive truth directly,
one can discover the goodness of God which guarantees
the reliability of the criterion.
Descartes' solution to the skeptical crisis brought
him immediate acclaim,
not only by his defenders but
also, and more particularly, by such critics
as Mer-
senne, Gassendi, and Hobbes. But in
spite of the sever-
ity of the attacks on his
views, his solution to the
skeptical crisis pushed out of sight an
alternative to
it, a solution which in the long run triumphed over
his
own.
Constructive skepticism—the lasting contribution of
the
seventeenth century to the “scientific attitude” and
to contemporary philosophy—admits the full force of
the
skeptical attack on necessary and certain knowl-
edge, but allows for a lesser knowledge about appear-
ances. Mersenne and Gassendi on the Continent and
Chillingworth in England first formulated the view
later worked out by some
early members of the Royal
Society of London and fully articulated by John
Locke
but not accepted until the collapse of the dogmatism
of
Descartes.
Marin Mersenne was trained at the Jesuit school at
La Flèche and
later joined the Order of Minîmes. A
great part of his life was
devoted to publicizing the
“new science.” His
writings are an attempt to show
the importance of science despite the
attacks of the
skeptics. His book, La
Vérité des sciences (1625), argues
that
even if the skeptic cannot be refuted we have a
wealth of knowledge suited
to our purposes in life.
Such knowledge consists of information about appear-
ances: hypotheses can be made about
the connections
of events and predictions made of the future course
of
experience. Science and mathematics do not yield
knowledge about any
transcendent reality or make any
metaphysical claims or depend upon any
such claims,
as both Bacon and Descartes had maintained.
Mersenne is fully conscious of the skeptics' attack
on knowledge. His
position is not that we do not know
anything but only that some things are
unknown. Ap-
pearances and effects can be
known, though we do not
know their real causes. Our senses do not inform
us
about the real natures of things but this does not pre-
vent formulation of laws—such as those of refrac-
tion—which enable us to
predict future experiences
and account for observed events. Despite the
disagree-
ments men have, which
Mersenne cannot but ac-
knowledge, there are
many agreements among them
too, and it is this that the skeptic overlooks.
Against the claim of the skeptic that everything is
a matter of controversy
Mersenne replies that many
things are never disputed. Against the claim
that all
arguments lead to an infinite regress (in the search for
premisses to support premisses) Mersenne claims that
there are some self-evident premisses and that predic-
tions can be checked empirically to
determine the
accuracy of the argument. In reply to the skeptic's
claim that syllogistic reasoning is unreliable because
there is no
guarantee that any set of premisses guaran-
tees its conclusion, he answers that we do judge of the
truth of
premisses and accept conclusions.
Mersenne's avowal of the extent of our knowledge
is not itself a claim that
complete certainty can be
attained. Indeed, in his Les
Questions théologiques
(1634) he presents his own
skeptical views. First, he
shows that knowledge of eternal truths is not
possible.
All we know is subject to doubt. There is no body of
demonstrative knowledge. He accepts the antimeta-
physical claims of the skeptic but also argues for
the
truth of science. The reliability of knowledge does not
depend on
discovering the grounds of all certainty. In
this sense both the dogmatist
and the skeptic are
mistaken—the one for claiming that
metaphysical
knowledge is possible and actual, the other for claiming
that it is not. Both are mistaken in assuming that sci-
ence depends upon a metaphysics and that metaphysi-
cal knowledge must be completely certain. Both
the
dogmatist and the skeptic are undermined. Between
their positions
lies a constructive path: doubting the
grounds but accepting the structure
of knowledge.
Not unlike the views of Mersenne were those of
Pierre Gassendi. Known best
as a critic of Descartes,
Gassendi actually rivalled him in popularity as a
scien-
tist and philosopher of science.
Well-read in the argu-
ments of the skeptics,
Gassendi rejected them as de-
featist and
negative because of the advances made in
the sciences in his own times. He
is credited with
introducing the distinction between primary and sec-
ondary qualities of objects into modern
philosophy,
thereby attacking the Aristotelian view that scientific
knowledge can both be based on sense perception and
be necessarily true. If
the observable properties of
things are not their real properties, there
can be no
necessarily true empirical knowledge. All we know are
the
appearances of things. As a disciple of the skeptical
tradition Gassendi
holds that all claims to knowledge
about the real world are unfounded and
that appear-
ances are the basis for all
knowledge. By experience
we cannot discover any general principles because
we
may always discover a negative instance. We observe
only the
appearances of things, not their real struc-
tures; hence we can make no inferences from appear-
ances to reality. However, to account for these phe-
nomena Gassendi reconstructed a version of
Epicurean
atomism—not as a metaphysics but as a set of theoret-
ical constructs to account for
appearances, a view
which Robert Boyle later characterized as the
“cor-
puscularean
hypothesis.” Such knowledge as we have
real structure of nature, though it gives a certainty
sufficient to make predictions about future experiences.
It is practically useful though not completely certain.
The views put forward by Mersenne and Gassendi
were generally not understood
by their contem-
poraries; further, they
were overshadowed by the
forcefulness of Descartes' position. It was not
until a
view somewhat like theirs was developed in England
that their
solution to the intellectual crisis of the time
could make its impact.
During the second and third decades of the century
there arose in England
what has become known as “the
Rule of Faith
controversy,” an outgrowth of the Refor-
mation controversy concerning the adequacy of each
church for
salvation. Each side used a battery of argu-
ments from the arsenal of skepticism to show that the
other side
could not guarantee its claim to religious
knowledge and truth. The
Catholic polemicists argued
that their opponents had no way of determining
which
book is the Bible, what it says, or what one ought to
do about
it. Protestants argued that the appeal by
Catholics to tradition and
authority was unreliable, and
that the average man had no way of
determining in-
fallibly what the tradition
was, the reliability of its
authority, nor even who was Pope.
Out of this controversy grew a form of constructive
or mitigated skepticism
that was able to deal with the
issues. The view is offered that
theoretically it might
not be possible to eradicate or overcome the
doubts
raised about the possibility of religious knowledge, but
that
there was a type of assurance that was sufficient
for practical religious
purposes. By using the standards
of common sense and practical life one
could attain
a limited amount of certainty—as much as the
case
admits of—a certainty that is beyond any
“reasonable
doubt” and sufficient for any
“reasonable man.”
One of the leading contenders in the Rule of Faith
controversy was the young
Anglican clergyman,
William Chillingworth, whose once famous book, The
Religion of Protestants, a Safe Way to Salvation
(1638),
deals with the theological issue of whether Protestants
have
any assurance of salvation outside the Catholic
Church. His opponents had
argued that there are only
two alternatives with respect to religious
knowledge:
either absolute certainty of the truths of faith or none
at
all. With respect to the first, Chillingworth argues
that such certainty is
not humanly attainable in reli-
gious matters,
though possible in mathematics and
metaphysics. Skeptical arguments against
the senses
and reason preclude such certainty. He is also un-
willing to accept the second alternative,
skepticism;
for such arguments, if taken too seriously, can destroy
all belief. He proposes instead that one can be reasona
bly certain of the doctrines necessary for salvation. The
assurance of common sense about everyday affairs is
made the standard for
solution to perplexities about
religion. The reasonable solution to any
problem is to
examine such evidence as is available and to proportion
assent to it. It became a cardinal principle to propor-
tion assent to evidence: to each kind of evidence
there
corresponds a kind or degree of assent, and as the
evidence is
greater or less so should be one's certainty.
In his description of the kinds of certainty a person
can have of the truth
of a statement Chillingworth is
not systematic. In the main he
distinguishes three levels
with their subclassifications or degrees: (1)
absolutely
infallible certainty, (2) conditionally infallible cer-
tainty, and (3) moral certainty. The first
of these—
presumably the kind of certainty Descartes sought
in
his Meditations—Chillingworth regards
as beyond
human reach. Such certainty excludes every possibility
of
doubt, a condition not attainable by mortal man.
Conditionally infallible
certainty is the highest attain-
able by man;
it is based upon such evidence as excludes,
for all human purposes, the
possibility of error, but
does not exclude it completely since all
experiences
may, for example, really be dream events. This kind
of
certainty occurs whenever one has knowledge, that
is, in those instances in
which, upon knowing the
meanings and connections of the terms involved,
assent
is compelled rather than voluntary. Because such
mathematical
truths as “the whole is greater than any
of its
parts” and “twice two is four” are of this
kind,
the certainty one has of their truth is called mathe-
matical certainty; similarly the
axioms of metaphysics
are said to be metaphysically certain. Such
infallible
certainty is possible not only for simple statements of
the
kinds of mentioned, but for demonstrations also, pro-
vided the rules of deductive inference are correctly
applied.
The third kind of certainty is moral certainty, the
certainty one has of
what is believed but not known.
This is the certainty of everyday life
about matters of
fact and is based on such evidence as excludes the
possibility of error for all practical purposes. The cer-
tainty one has when traveling that he is on the right
road and that the book one is reading is the work of
the person whose name
appears on the title page are
of this sort. Moral certainty is described as
the certainty
a sane, reasonable, and thoughtful person has after
considering all available evidence as fully and impar-
tially as is possible and giving his assent to that
side
on which the evidence seems strongest. Since belief
is based upon
a different kind of evidence than knowl-
edge,
and is therefore less certain, the possibility of
error is increased. As in
conditionally infallible cer-
tainty the dream
hypothesis prevents absolute certainty
doubt also operates, for “seeing the generality of men
is made up of particulars, and every particular man
may deceive and be deceived, it is not impossible,
though exceedingly improbable, that all men should
conspire to do so” (Chillingworth, pp. 203-04). If this
possibility were taken seriously life would soon fall
apart. If on grounds of possibility of error alone one
refused to accept the testimony of witnesses the trial
of criminal cases would soon become a shambles. Re-
jection on similar grounds of the reports of travelers
and chroniclers would soon turn history into fiction.
Although such possibilities exist, they are not destruc-
tive of the everyday activities of life; such beliefs as
one has of matters of fact—of routes, the reliability
of witnesses, and so on—suffice to get one through the
day. Many things of which one is only morally certain
may be true, but since the available evidence does not
warrant a claim to knowledge one need and can be
only as certain as the evidence allows. Unlike mathe-
matical certainty, moral certainty admits of degrees
because the strength of the evidence varies. Precisely
where the lines are to be drawn between the several
degrees of moral certainty, however, and what the
standard is by which the degrees are measured, are
not made clear.
The theoretical justification for accepting moral
certainty is that some
things by their very natures do
not admit of more than a specific kind and
amount
of evidence and therefore it is unreasonable to demand
more,
e.g., mathematical proof for a matter of fact.
The practical justification,
stated with respect to reli-
gious belief, is
that moral certainty suffices to turn the
sinner from the ways of darkness
to the path of light.
This view of the nature of certainty was developed
in the next generation by
several early members of the
Royal Society of London who were also
clergymen,
among them John Tillotson, Joseph Glanvill, and John
Wilkins. As so developed, especially by Wilkins and
Glanvill, the theory
was secularized, i.e., stated and
applied in the context of scientific
knowledge. Wilkins'
views are particularly instructive, for in them is
found
a formulation in the context of religion which was
applied to
scientific procedures by Royal Society
members and which later received
full expression in
the writings of John Locke. Its application to
scientific
procedures was due largely to Wilkins' influence in
founding the Royal Society and in formulating its
policy.
After taking a degree at Oxford in 1634 Wilkins took
orders and rose rapidly
in the Church of England—in
part because of political influence.
One of his major
interests was in science. Though not of the
prominence
of such of his friends as Boyle, Hooke, Wallis, and
Barrow, he nevertheless took a keen interest in several
of the
particular sciences. More important than his role
as an amateur scientist
was his association with the
Royal Society. It is known that he attended
scientific
meetings of the Invisible College in London as early
as
1645, and that he initiated a new series of meetings
in Oxford when he
moved there. Later, in 1660, he
presided over the meeting in which formal
action was
taken to establish a society. He held offices in and was
active in the Royal Society until his death.
Wilkins' major work, Of the Principles and Duties
of
Natural Religion, was published posthumously in
1675. In it he
sees knowledge characterized by the
same extremes as had Chillingworth,
absolute certainty
and extreme skepticism. He acknowledges the
ideality
of the first but realizes that it cannot be attained be-
cause of the limitations of the human
faculties. The
second alternative is at all costs to be avoided,
because
acceptance of “the cavils of Sceptical captious
Men”
would put an end to the certainty of religious and
scientific belief and of the beliefs of everyday life, none
of which
Wilkins is willing to forego. He is not willing,
as was Descartes, to
reject everything for which the
conditions of falsity can be stated; such
skepticism leads
to nihilism and is therefore rejected as absurd.
Wilkins
admits at the outset that the structure of reality cannot
be
completely understood by the human mind, but does
not take this as a reason
for despair.
The antiskeptical theme is an important one in his
book on religion, in
which the major question for
consideration is, how can religious belief be
justified
without capitulation to the arguments of the skeptic?
Wilkins' solution is a development of the theory of
probable certainty
stated earlier by Chillingworth. In
general, he disregards the arguments of
the skeptic and
bases his theory of religious knowledge on the fact
that
ordinary people are not seriously affected by such
arguments. In
their daily and practical affairs people
do claim certainty and base it on
evidence. He tries
to discover what kinds of certainty they claim,
together
with the corresponding kinds and levels of evidence.
In his
classification, a scheme later used by Locke in
his Essay
Concerning Human Understanding (IV, xiv-
xv), two levels of assent are distinguished. On the one
hand there
is knowledge, “... which doth arise from
such plain and clear
Evidence as doth not admit of
any reasonable cause of doubting”
(Wilkins, p. 5).
Three subclassifications are made: physical, mathe-
matical, and moral certainty. On the
other hand there
is probability, “... which doth arise from such
Evi-
dence as is less plain and
clear” (Wilkins, p. 8). Beneath
these, where the evidence is
such as to warrant neither
affirmation nor denial, there is simply
hesitation or
suspension of judgment.
On another scheme of classification, which follows
Chillingworth's text more
closely, three levels of cer-
tainty are
distinguished: absolutely infallible certainty,
conditionally infallible
certainty, and indubitable cer-
tainty. The
first is the prerogative of God. The second
comprises both physical and
mathematical certainty
and is the greatest humanly possible (revelation
possi-
bly excepted). Such certainty
presupposes fulfillment
of two requirements, that “our faculties
be true, and
that we do not neglect the exerting of them”
(Wilkins,
p. 9). Wilkins sets down their fulfillment as a postulate
without which knowledge is impossible. The third
level, indubitable
certainty, which is the same as moral
certainty, is not as strong as
infallible certainty for,
although the same suppositions are made, the
evidence
is less strong and thus provides only an assurance
“which doth not admit of any reasonable cause of
doubting.”
Each of these kinds of certainty is clarified by an
examination of the
evidence to which each is supposed
to be correlated. In doing this Wilkins
tries to be
precise and so defines his crucial terms, though his
meanings are not always clear. He begins with the
senses and distinguishes
the external from the internal.
The senses are the source of the highest
certainty of
which man is capable, physical certainty, but they are
not infallible. Wilkins admits that he does not know
how the senses
operate, but claims that this is no
argument against the genuineness of the
knowledge
derived from them. The causes of sense perception are
one
thing, the results another, and difficulties about
the one do not
necessarily bode ill for the other.
The second kind of evidence Wilkins considers—
evidence from the
nature of things—relates to the
function of the understanding
and (at its best) gives
rise to mathematical certainty. Mathematical
certainty
is the kind of assurance one has of the propositions
and
demonstrations of mathematics and other abstract
sciences. Upon knowing the
meanings of the terms
involved no one could deny without contradiction
that
the whole is greater than the part or that three plus
three
equals six. There occurs here what Wilkins calls
“natural
necessity”; one could no more deny this sort
of proposition than
he could avoid feeling hungry or
sleepy. Denial of such propositions as
these would be
self-contradictory for it would be to deny meanings
already accepted. Evidence from the nature of things
occurs
“when there is such a Congruity or Incongruity
betwixt the Terms
of a Proposition, or the Deduction
of one Proposition from another, as doth
either satisfy
the mind, or else leaves it in doubt and hesitation
about
them” (Wilkins, p. 4).
Moral or indubitable certainty follows mathematical
certainty. Of the three
major kinds of certainty Wilkins
recognizes this is the most important since of most
things said
to be known one can at best be only morally
certain. By it he runs the
middle course between abso-
lute certainty and
complete uncertainty. Moral cer-
tainty is the
assurance one has of anything for which
there is no ground for a
“reasonable doubt.” In making
reasonable doubt the
distinguishing feature of moral
certainty Wilkins is making an appeal to
common
sense. In the context of religion in which he is writing
the
skeptic and dogmatist are both unreasonable, the
one for making the bare
possibility of doubt a sufficient
reason for withholding assent, and the
other for de-
manding a kind of evidence not
open to any doubt
whatever. Wilkins makes an appeal to what the man
in
the street believes, and makes this the standard by
which to solve his
problems: whatever is unacceptable
to the common and reasonable man is
probably not
true. This appeal is made in two ways. First, the exam-
ples he uses are drawn from the ordinary
affairs of life:
the reports of travelers, merchants, and the like.
“I
appeal to the common judgment of mankind,”
says
Wilkins. Secondly, the kind of certainty appealed to
is that of
the reasonable man. What an ordinary person,
possessed of all his faculties
and judicious in his use
of evidence, would accept as true is for Wilkins
the
standard of truth.
The principle of reasonable doubt leaves open the
possibility that what has
been proved may be otherwise
than the evidence indicates; however, this is
not a
sufficient reason for withholding assent. “Who is
there
so wildly skeptical as to question,” asks Wilkins,
“whether the Sun shall rise in the East, and not in the
North,
or West, or whether it shall rise at all?” No
one can doubt such
things without abandoning ration-
ality.
Acceptance of less than infallible certainty is a
principle so strong in
human nature that if it were
otherwise reason would be a torment to
mankind. Men
would be soon driven to insanity if the mere possibility
of error were a suitable basis on which to establish
one's doubts or
beliefs.
The evidence giving rise to moral certainty is that
of the senses or of the
nature of things when the senses
are not adequate to give rise to higher
levels of cer-
tainty. Particularly relevant
to belief in matters of fact
beyond one's immediate experience is
testimony. The
testimony of witnesses to a crime, of an explorer to
the customs of a distant country, or of an historian
to events in the past
are all adequate bases for belief,
provided that the witnesses are
authoritative and cred-
ible. The criteria for
determining competence are not,
however, spelled out by Wilkins.
In laying the groundwork for his discussion of natural
religion Wilkins
proceeds, after considering the kinds
of evidence and certainty, to
establish their relationship
degrees of truth; truth does not admit of more or less.
Historical and geographical statements are as true as
those of mathematics and metaphysics. The problem
is that the same kind of evidence cannot be produced
for each. But to deny the truth of an historical proposi-
tion because it cannot be immediately verified in sense
experience or by demonstration (and thus not infallibly
certain) would involve the gross error of supposing that
because all truths are on a par the evidence must be
so too. Wilkins cites in this connection a passage from
Aristotle's Nicomachean Ethics (I, 3) in which it is
pointed out that where there are differences in the
subject matter to be proved the kind of evidence must
be expected to differ. Paraphrasing Aristotle, Wilkins
points out that it would be absurd to use a rhetorical
speech to prove a mathematical proposition and
equally out of place to use a demonstrative argument
to arouse the emotions of an audience. This principle
is Wilkins' ultimate justification for accepting less than
infallible certainty in religion and the sciences. So long
as any proof is good in its kind and suited to the subject
matter, its conclusion is justified.
The account of constructive skepticism worked out
by Chillingworth and
Wilkins with respect to religious
knowledge was not restricted to that
domain. There
is evidence to show that even in Wilkins' writings an
effort is made to extend it to scientific knowledge as
well. The writings
of several of his contemporaries
contain views on evidence and certainty
remarkably
similar to those Wilkins held. In the
“experimental
philosophy” of the Royal Society
scientific conclusions
are not taken to be absolutely true but as
probable
only. Such conclusions are subject to revision upon
discovery
of new evidence. The ideal of science as a
deductive system is recognized
for what it is, an ideal
not attainable in practice because of the
limitations
of our faculties and the complexity of nature. Science
does not make known the real structure of things but
formulates hypotheses
to account for what is ob-
served—a
redevelopment of the account put forward
by Mersenne and Gassendi.
This account of certainty as applied to scientific
conclusions was detailed
by such early members of the
Royal Society as Joseph Glanvill and Robert
Boyle.
Whereas Glanvill was primarily concerned with the
theory of
science, Boyle applied this account of cer-
tainty to his own scientific conclusions. However, much
of Boyle's
exposition of the theory is still in the context
of religion; the majority
of his comments on the nature
and extent of knowledge occur in his
theological writ-
ings. In the writings of
Isaac Newton the situation is
somewhat different. Here there is little
discussion of
a theory of knowledge though a theory is assumed in
his scientific writings. Whereas most of his contem-
poraries in the Royal Society had
been explicit in their
views on the limitations of knowledge and the
levels
of certainty, Newton has little to say on these points.
According to him there are some things the scientist
finds beyond the reach
of intellect and whose natures
must be acknowledged as unknown,
particularly the
natures of light and gravity and of physical bodies,
though speculative hypotheses can be formulated to
account for them.
In his early contributions to the Philosophical Trans-
actions concerning the
analysis of light Newton says
that his views are certain; however, it is an
account
only of the rays of light as they appear to the observer
and
not as they are in themselves. “But, to determine
more
absolutely, what light is, after what manner re-
fracted, and by what modes or actions it produceth
in our minds
the Phantasms of Colours, is not so easie.
And I shall not mingle
conjectures with certainties”
(Phil.
Trans. No. 80 [19 February 1671/72]). To give
an account of the nature
of light would be to formulate
a speculative hypothesis, a conjecture which
has no
role in the presentation of the results of scientific in-
quiry. Though he sought to discover the nature
of light
he was not successful in doing so. Hence he limited
himself
to a descriptive account of how light is bent,
refracted, and so on.
As in the case of light, so also the force of gravity
is unknown. In spite
of this Newton did manage to
formulate some significant laws describing the
motions
of bodies as affected by gravity. That such significant
results can be achieved, it should be noted, is an appli-
cation of the perspective taken earlier by Mersenne
and Gassendi. Again, our knowledge of bodies is limited
to an acquaintance
with their secondary qualities, not
their real natures. Shapes, colors,
tactile qualities, and
the like can be observed but “their
inward substances
are not to be known either by our senses or by any
reflex act of our minds” (Newton, Mathematical
Princi-
ples..., p. 546). The
world of primary qualities is
beyond our grasp, though one can formulate an
hy-
pothesis about them. Newton's
hypothesis is not unlike
the atomism of Boyle and Gassendi.
Newton's predecessors and contemporaries in the
Royal Society had delineated
with care several levels
of certainty, each corresponding to a particular
kind
of evidence. At the summit was usually the certainty
of immediate
sense perception or that of mathematics
or metaphysics. Next were the
several degrees of mor-
ally certain
propositions, which class usually contained
those of science and religion.
At the bottom was mere
probability. Boyle, for example, works out such
an
hierarchical view. One can never be completely certain
of the
conclusions of the sciences because of the limita-
God may change the course of nature (as occurs in
miracles) at the very moment we formulate laws. Sci-
entific conclusions for Boyle give rise to physical cer-
tainty when all conditions are at their best, but this
is an ideal seldom achieved. Generally, such conclu-
sions are only morally certain. Both of these kinds of
certainty, he says, are “but an inferior kind or degree
of certainty.” He regards the attempt of Descartes and
other physicists, for example, to prove that certain
comets are not meteors on the ground and that their
parallax is less than that of the moon, to have only
a moral certainty for they have not themselves made
the relevant observations.
Newton is much less explicit in his presentation,
distinguishing only
mathematical propositions from
those that are physically certain, and
pointing out that
scientific statements are not mathematically
certain.
What the scientist regards as true may in fact turn
out to be
false since his conclusions are based upon
merely human principles. Science
cannot provide an
explanatory account of the real structure of nature
but
must limit itself to a descriptive account of what is
observed to
occur, and its conclusions are less than
absolutely or demonstratively
certain. In his contro-
versy with Robert
Hooke concerning the nature of light
he admits his conclusions are only
physically certain
because of limitations in the evidence. One begins
with
evidence that can be expressed in mathematical for-
mulae and from these deduces the existence of other
phenomena to be observed. The conclusions of one's
inferences are no more
certain than the premisses from
which one begins; if these are inductive
generalizations
one's conclusions have no greater certainty.
Newton's account of what can be known is applied
by him to religion as well
as to science. One of the
features of the movement in English thought that
we
have been tracing concerns the close relation between
evidence for
religious and for scientific propositions.
In Chillingworth's writings
references to scientific
knowledge occurred only incidentally; in
Wilkins'
writings such references were of fundamental impor-
tance. The point was often made that the
canons of
evidence which held for one also held for the other.
In
Newton's thought the relation between religion and
science also plays a
significant role. Indeed, for him
the pursuit of scientific truth has as
one of its ultimate
justifications insight into religious truth. The first
of
his letters to Richard Bentley begins with the comment
that the
complexity of nature can be accounted for
only by reference to a deity with
mathematical in-
genuity. In one of the
Scholia to the Mathematical
Principles of Natural
Philosophy (1687) he notes, “And
so much concerning
God, to discourse of whom from
the appearances of things, does certainly belong to
Natural
Philosophy” (Newton, p. 546). Newton's point
seems to be that if
the evidence for scientific and
religious propositions is of the same kind,
then the
certainty for each will be the same also.
Such then is the reply of the seventeenth-century
mind to the crisis of
skepticism. Two major alternatives
are worked out: the dogmatism of Bacon
and Descartes
on the one side and the constructive skepticism of
Mersenne, Gassendi, Chillingworth, and the early
members of the Royal
Society of London on the
other—a view which, after the middle of
the eight-
eenth century, became the accepted
account of cer-
tainty in all domains of
knowledge. In the final decade
of the seventeenth century John Locke
formulated an
account of the extent and certainty of knowledge
which
articulates for all knowledge—not merely sci-
entific and religious knowledge—the
constructive
skepticism we have been examining. But Locke's the-
ory of the certainty of knowledge also
included some
elements of the Cartesian epistemology, a blending
which
gave rise to a new series of problems for eight-
eenth-century thought.
BIBLIOGRAPHY
Francis Bacon, Novum Organum, in The Works of Francis
Bacon, eds. J. Spedding, R.
L. Ellis, and D. D. Heath, 15
vols. (Boston, 1861). William
Chillingworth, The Works of
William Chillingworth,
containing his book The Religion of
Protestants, a Safe Way to
Salvation (Philadelphia, 1844).
John Dewey, The Quest for Certainty (New York, 1960,
reprint).
René Descartes, The Philosophical Works of Des-
cartes, eds. E
. S. Haldane and
G. R. T. Ross, 2 vols.
(New York, 1955). John Locke, Essay Concerning Human
Understanding (1690; London and New
York, 1924; many
reprints). Marin Mersenne, La
Vérité des sciences contre les
sceptiques ou
pyrrhoniens (Paris, 1623); idem, Les
Questions
théologiques, physiques, morales et
mathématiques (Paris,
1634). Isaac Newton, Mathematical Principles of Natural
Philosophy and his
System of the World, trans. A. Motte
(1729); rev. by F. Cajori
(Berkeley; 1946). The Philosophical
Transactions of
the Royal Society of London, eds. C. Hutton,
G. Shaw, and R.
Pearson, 18 vols. (London, 1809). Richard
H. Popkin, The History of Scepticism from Erasmus to
Descartes (New
York, 1961). Henry G. Van Leeuwen, The
Problem of
Certainty in English Thought 1630-1690 (The
Hague, 1963). John
Wilkins, Of the Principles and Duties
of Natural
Religion (London, 1699).
HENRY G. VAN LEEUWEN
[See also Appearance and Reality; Axiomatization; Baco-nianism; Causation; Certainty since the Seventeenth Cen-
tury; Faith; Indeterminacy; Necessity; Newton on Method;
Rationality; Reformation; Sin and Salvation; Skepticism.]
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