formed from ὑπό, under, and θέσις, position, from θέω, 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.

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 second 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, and the former a thesis.

In strict logic, we are never to pass from the hypothesis to the thesis; that is, the principle supposed must be proved to be true, before we require the consequence to be allowed.

It has become common, since the time of Newton, to decry all reasoning from hypotheses, as useless and unphilosophical. But was not the theory of gravitation itself founded upon a conjecture, that is, upon an hypothesis? It was founded upon the supposition that the power which regulates the fall of heavy bodies also regulates the motion of the moon; a supposition upon which he proceeded to reason before it was verified by calculation. The subject of the use and abuse of hypotheses in philosophical inquiries has been admirably illustrated by Mr Stewart, in the second volume of his Philosophy of the Mind; and to that book we refer those who wish to form accurate notions on this subject.