One _person_, and things innumerable! As we look about us, we find the horizon peopled with thousands and millions and infinite quantities of objects, which may one by one attract our attention, and may be gathered up in the vast, unbounded picture surveyed by the eye as it moves on from thing to thing, incessantly, without ever reaching the last. The world which we first discover is the world of matter, of things which strike our senses. This world rushes impetuously into our mind at the beginning of our natural experience. And these material objects are many not only _de facto_ but also _de jure_. They must be, they cannot but be many if we are to consider them as material things. It is their peculiar nature, it is their very essence to be an indefinite multitude. A material thing means a thing occupying space. And space is made up of elements, each one of which excludes all the others and is therefore conceived independently of the others, must so be conceived. For it is the very nature of space to be divisible. When it is narrowed down to a point and cannot be further subdivided, then it ceases to be space. Its divisibility signifies that space is nothing more than the sum of its parts; that it contains nothing in addition to these parts; that it therefore resolves itself into them without at all losing its being and without any of the parts being deprived of anything which was theirs in the whole. In fact, if anything were lost of the entire whole, this loss could not but be felt in each single part. A book, considered as a material thing, is composed of a certain number of printed leaves stitched together; and if the leaves fall apart, they may be brought together again so that they will compose the same book as before. An iron rod weighs the same before and after it has been broken up into parts.