(formed of ὑπό under, and ἔχω pono, "I put"), is a proposition or principle which we suppose, or take for granted, in order to draw conclusions for the proof of a point in question.

In disputation, they frequently make false hypotheses, in order to draw their antagonists into absurdities; and even in geometry truths are often deducible from such false hypotheses.

Every conditional or hypothetical proposition may be distinguished into hypothesis and thesis: the first rehearses the conditions under which any thing is affirmed or denied; and the latter is the thing itself affirmed or denied. Thus, in the proposition, a triangle is half of a parallelogram, if the bases and altitudes of the two be equal; the latter part is the hypothesis, "if the bases," &c., and the former a thesis, "a triangle is half a parallelogram."

In strict logic, we are never to pass from the hypo-

in Physics, &c., denotes a kind of system laid down from our own imagination, whereby to account for some phenomenon or appearance of nature. Thus we have hypotheses to account for the tides, for gravity, for magnetism, for the deluge, &c.

The real and scientific causes of natural things generally lie very deep; observation and experiment, the proper means of arriving at them, are in most cases extremely slow, and the human mind is very impatient; hence we are frequently driven to feign or invent something that may seem like the cause, and which is calculated to answer the several phenomena, so that it may possibly be the true cause.

Philosophers are divided as to the use of such fictions or hypotheses, which are much less current now than they were formerly. The latest and best writers are for excluding hypotheses, and standing wholly on observation and experiment. Whatever is not deduced from phenomena, says Sir Isaac Newton, is an hypothesis; and hypotheses, whether metaphysical, or physical, or mechanical, or of occult qualities, have no place in experimental philosophy.

The Cartesians take upon them to suppose what affections in the primary particles of matter they please; just what figures, what magnitudes, what motions, and what situations, they find for their purpose. They also feign certain unseen, unknown fluids, and endue them with the most arbitrary properties; give them a subtilty which enables them to pervade the pores of all bodies, and make them agitated with the most unaccountable motions. But is not this to set aside the real constitution of things, and to substitute dreams in their place? Truth is scarce attainable even by the surest observations; and will fanciful conjectures ever come at it? They who found their speculations on hypotheses, even though they argue from them regularly, according to the strictest laws of mechanics, may be said to compose an elegant and artful fable; but it is still only a fable.

HYPOTHESIS is more particularly applied in astronomy to the several systems of the heavens; or the different ways in which different astronomers have supposed the heavenly bodies to be ranged, moved, &c.

The principal hypotheses are the Ptolemaic, Copernican, and Tychoonic. The Copernican is now become so current, and is so well warranted by observation, that the retainers thereto hold it injurious to call it an hypothesis. See ASTRONOMY.