though it be not altogether so certain as our intuitive knowledge, or
the deductions of our reason employed about the clear abstract ideas
of our own minds; yet it is an assurance that deserves the name of
KNOWLEDGE. If we persuade ourselves that our faculties act and inform
us right concerning the existence of those objects that affect them, it
cannot pass for an ill-grounded confidence: for I think nobody can, in
earnest, be so sceptical as to be uncertain of the existence of those
things which he sees and feels. At least, he that can doubt so far,
(whatever he may have with his own thoughts,) will never have any
controversy with me; since he can never be sure I say anything contrary
to his own opinion. As to myself, I think God has given me assurance
enough of the existence of things without me: since, by their different
application, I can produce in myself both pleasure and pain, which
is one great concernment of my present state. This is certain: the
confidence that our faculties do not herein deceive us, is the greatest
assurance we are capable of concerning the existence of material beings.
For we cannot act anything but by our faculties; nor talk of knowledge
itself, but by the help of those faculties which are fitted to apprehend
even what knowledge is.

But besides the assurance we have from our senses themselves, that they
do not err in the information they give us of the existence of things
without us, when they are affected by them, we are further confirmed in
this assurance by other concurrent reasons:--


4. I. Confirmed by concurrent reasons:--First, Because we cannot have
ideas of Sensation but by the Inlet of the Senses.

It is plain those perceptions are produced in us by exterior causes