The propensity to seek for principles in the common usages of language may be discerned at a very early period. Thus we have an example of it in a saying which is reported of Thales, the founder of Greek philosophy.[13\1] When he was asked, "What is the _greatest_ thing?" he replied, "_Place_; for all other things are _in_ the world, but the world is _in_ it." In Aristotle we have the consummation of this mode of speculation. The usual point from which he starts in his inquiries is, that we say thus or thus in common language. Thus, when he has to discuss the question, whether there be, in any part of the universe, a Void, or space in which there is nothing, he inquires first in how many senses we say that one thing is _in_ another. He enumerates many of these;[14\1] we say the part is in the whole, as the finger is _in_ the hand; again we say, the species is in the genus, as man is included _in_ animal; again, the government of Greece is _in_ the king; and various other senses are described or exemplified, but of all these _the most proper_ is when we say a thing is _in_ a vessel, and generally, _in place_. He next examines what _place_ is, and comes to this conclusion, that "if about a body there be another body including it, it is in place, and if not, not." A body _moves_ when it changes its place; but {64} he adds, that if water be in a vessel, the vessel being at rest, the parts of the water may still move, for they are included by each other; so that while the whole does not change its place, the parts may change their places in a circular order. Proceeding then to the question of a _void_, he, as usual, examines the different senses in which the term is used, and adopts, as the most proper, _place without matter_; with no useful result, as we shall soon see. [Note 13\1: Plut. _Conv. Sept. Sap._ Diog. Laert. i. 35.] [Note 14\1: Physic. Ausc. iv. 3.] Again,[15\1] in a question concerning mechanical action, he says, "When a man moves a stone by pushing it with a stick, _we say_ both that the man moves the stone, and that the stick moves the stone, but the latter _more properly_." [Note 15\1: Physic. Ausc. viii. 5.] Again, we find the Greek philosophers applying themselves to extract their dogmas from the most general and abstract notions which they could detect; for example,--from the conception of the Universe as One or as Many things. They tried to determine how far we may, or must, combine with these conceptions that of a whole, of parts, of number, of limits, of place, of beginning or end, of full or void, of rest or motion, of cause and effect, and the like. The analysis of such conceptions with such a view, occupies, for instance, almost the whole of Aristotle's _Treatise on the Heavens_.