We have seen that our very thoughts, and therefore consciousness of living, are limited by Time and Space, but we cannot with the utmost endeavour conceive a limit to Time and Space; they are two twin sisters, alike in many respects but different in others, and we shall realise later on that they are readily interchangeable. The sensuous aspect of Motion is, as we have seen, the time that an object takes to go over a certain space--namely, what is called the rate at which it passes from one point to another, and we cannot imagine Motion unless it contains both of these modes in however small a quantity; we may have the greatest imaginable space traversed in a moment of time, or the smallest imaginable space covered in what may be called, for want of a better word, an eternity, but we still have to postulate what we call Motion; this, of course, follows from the fact that our thoughts require both these modes for forming concepts. If we compare our conception of Matter with that of Time and Space, we see that the two latter are not separately the object of any sense, but are the modes or conditions under which all our senses act, to a greater or less degree, and these conditions cannot therefore carry the same impression of objectivity to our senses as Matter does, except perhaps in the sense that all physical phenomena are simply motion, and motion is the product of both of these limitations but not of either of them separately. If we analyse our conceptions of Time and Space we seem forced to postulate that they are both infinitely divisible and infinitely extensible; they are both what is called continuous and not discrete, we cannot conceive any minimum in their division; both duration in Time and extension in Space can be reduced, as it were, to a mathematical point; nor can we conceive any maximum in either duration or extension. They are both therefore comprised in every conception possible to our consciousness; all parts of Time are time and all parts of Space are space; there are no holes, as it were, in Space which are not space, nor intervals in Time which are not time, they are both complete units; Space cannot be limited except by space, and Time cannot be limited except by time. So far they are alike, but, on the other hand, Space is comprised of three dimensions--namely, length, breadth, and depth, whereas Time has the appearance to us of comprising one dimension only--namely, length. Under our present conditions we can only think of one finite subject at a time, and, at that moment, all other subjects are cancelled. We can therefore only think of points in Time and Space as situated beyond, or in front of, other fixed points, which again must be followed by other points; we cannot fix a point in either so as to exclude the thought of a point beyond; we can only in fact examine them in a form of finite sequences.