called intuitive knowledge. Thus we see that red is not green; that the whole is bigger than a part; and that two and two are equal to four.
The truth of these and the like propositions we know by a bare simple intuition of the ideas themselves, without any more ado; and such propositions are called self-evident.
The mediate perception of the agreement or disagreement of two ideas is, when, by the intervention of one or more other ideas, their agreement or disagreement is shown. This is called demonstration, or rational knowledge. For instance, the inequality of the breadth of two windows, or two rivers, or any two bodies that cannot be put together, may be known by the intervention of the same measure applied to them both; and so it is in our general ideas, whose agreement or disagreement may be often shown by the intervention of some other ideas, so as to produce demonstrative knowledge; where the ideas in question cannot be brought together, and immediately compared, so as to produce intuitive knowledge.
The understanding doth not know only certain truth; but also judges of probability, which consists in the likely agreement or disagreement of ideas.
The assenting to any proposition as probable is called opinion, or belief.
We have hitherto considered the great and visible parts of the universe, and those great masses of matter, the stars, planets, and particularly this our earth, together with the inanimate parts, and animate habitants of it; it may be now fit to consider what these sensible bodies are made of, and that is of unconceivably small bodies or atoms, out of whose various combinations bigger moleculæ are made: and so, by a greater and greater composition, bigger bodies; and out of these the whole material world is constituted.
By the figure, bulk, texture, and motion, of these small and insensible corpuscles, all the phenomena of bodies may be explained.
