2. Wherein reasoning consists.
If general knowledge, as has been shown, consists in a perception of the agreement
or disagreement of our own ideas, and the knowledge of the existence of all things without us (except only of a
God, whose existence every man may certainly know and demonstrate to himself from his own existence), be had
only by our senses, what room is there for the exercise of any other faculty, but outward sense and inward
perception? What need it there of reason? Very much: both for the enlargement of our knowledge, and regulating
our assent. For it hath to do both in knowledge and opinion, and is necessary and assisting to all our other
intellectual faculties, and indeed contains two of them, viz., sagacity and illation. By the one, it finds out; and by
the other, it so orders the intermediate ideas as to discover what connexion there is in each link of the chain,
whereby the extremes are held together; and thereby, as it were, to draw into view the truth sought for, which is
that which we call illation or inference, and consists in nothing but the perception of the connexion there is
between the ideas, in each step of the deduction; whereby the mind comes to see, either the certain agreement or
disagreement of any two ideas, as in demonstration, in which it arrives at knowledge; or their probable connexion,
on which it gives or withholds its assent, as in opinion. Sense and intuition reach but a very little way. The
greatest part of our knowledge depends upon deductions and intermediate ideas: and in those cases where we are
fain to substitute assent instead of knowledge, and take propositions for true, without being certain they are so, we
have need to find out, examine, and compare the grounds of their probability. In both these cases, the faculty
which finds out the means, and rightly applies them, to discover certainty in the one, and probability in the other,
is that which we call reason. For, as reason perceives the necessary and indubitable connexion of all the ideas or
proofs one to another, in each step of any demonstration that produces knowledge; so it likewise perceives the
probable connexion of all the ideas or proofs one to another, in every step of a discourse, to which it will think
assent due. This is the lowest degree of that which can be truly called reason. For where the mind does not
perceive this probable connexion, where it does not discern whether there be any such connexion or no; there
men's opinions are not the product of judgment, or the consequence of reason, but the effects of chance and
hazard, of a mind floating at all adventures, without choice and without direction.
