The use of words being to stand as outward marks of our internal ideas, and those ideas being taken from particular things, if every particular idea that we take in should have a distinct name, names must be endless. To prevent this, the mind makes the particular ideas received from particular objects to become general, which is done by considering them as they are in the mind, and such appearances separate from all other existences, and from the circumstances of real existence, as time, place, or any other concomitant ideas. This is called Abstraction, whereby ideas taken from particular being become general representatives of all of the same kind. Thus, the same colour being observed to-day in chalk or snow which the mind yesterday received from milk, it considers that that appearance alone makes it a representative of all of that kind; and having given it the name "whiteness," it by that sound signifies the same quality wheresoever imagined or met with; and thus universals, whether ideas or terms, are made.
As the mind is wholly passive in the reception of all its simple ideas, so it exerts several acts of its own, whereby, out of its simple ideas, as the materials and foundations of the rest the others are framed. And I believe we shall find, if we observe the originals of our notions, that even the most abstruse ideas, how remote soever they may seem from sense, or from any operation of our minds, are yet only such as the understanding frames to itself, by repeating and joining together ideas that it had either from objects of sense or from its own operations about them; so that even those large and abstract ideas are derived from sensation or reflection, being no other than what the mind may and does attain by the ordinary use of its own faculties.
IV.—Knowledge of the Existence of Other Things
It is the actual receiving of ideas from without that gives us notice of the existence of other things, and makes us know that something does exist at that time without us which causes that idea in us, though perhaps we neither know nor consider how it does it. And this, though not so certain as our own intuitive knowledge, or as the deductions of our reason employed about the clear abstract ideas of our own minds, yet deserves the name of knowledge.
It is plain that those perceptions are produced by exterior causes affecting our senses for the following reasons.
Because those that want the organs of any sense never can have the ideas belonging to that sense produced in their minds.
Because sometimes I find I cannot avoid having those ideas produced in my mind; for as when my eyes are shut, or the windows fast, I can at pleasure recall to my mind the ideas of light or the sun which former sensations have lodged in my memory; so I can at pleasure lay by that idea and take into my view that of a rose or taste of sugar. But if I turn my eyes at noon towards the sun, I cannot avoid the ideas which the light or sun produces in me. There is nobody who does not perceive the difference in himself contemplating the sun as he has an idea of it in his memory and actually looking upon it; and, therefore, he has certain knowledge that they are not both memory or the actions of his mind and fancies only within him, but that actual seeing has a cause without.
Add to this that many of those ideas are produced with pain, which afterwards we remember without the least offence.
Lastly, our senses bear witness to the truth of each other's report concerning the existence of sensible things without us.