11. Past existence of other things is known by memory.
As when our senses are actually employed about any
object, we do know that it does exist; so by our memory we may be assured, that heretofore things that affected
our senses have existed. And thus we have knowledge of the past existence of several things, whereof our senses
having informed us, our memories still retain the ideas; and of this we are past all doubt, so long as we remember
well. But this knowledge also reaches no further than our senses have formerly assured us. Thus, seeing water at
this instant, it is an unquestionable truth to me that water doth exist: and remembering that I saw it yesterday, it
will also be always true, and as long as my memory retains it always an undoubted proposition to me, that water
did exist the 10th of July, 1688; as it will also be equally true that a certain number of very fine colours did exist,
which at the same time I saw upon a bubble of that water: but, being now quite out of sight both of the water and
bubbles too, it is no more certainly known to me that the water doth now exist, than that the bubbles or colours
therein do so: it being no more necessary that water should exist to-day, because it existed yesterday, than that the
colours or bubbles exist to-day, because they existed yesterday, though it be exceedingly much more probable;
because water hath been observed to continue long in existence, but bubbles, and the colours on them, quickly
cease to be.
