— things also pass from one part of the order or of a number to the other, when, for example, the first becomes the second and the second the third, etc. In fact, time and space are only kinds of order, and in these orders the vacant place (which in relation to space is called vacuum), if there were any, would show the possibility only of that which is lacking together with its relation to the actual. Ph. I am nevertheless very glad that you agree with me that matter does not change in volume. But you seem to go too far, sir, in not recognizing two extensions, and you resemble the Cartesians, who do not distinguish space from matter. Now it seems to me that if a class is found who, not having these distinct ideas (of space and of solidity which fills it), blends them and makes of the two one only, we cannot see how these persons can converse with others. They are like a blind man who, when another man speaks to him of scarlet, thinks it resembles the sound of a trumpet. Th. [But I hold at the same time that the ideas of extension and solidity, like that of scarlet-colour, do not consist in an I know not what. I distinguish extension and matter, contrary to the view of the Cartesians. Still I do not believe that there are two extensions; and since those who dispute over the difference between extension and solidity are agreed on several truths upon this subject and have some distinct notions, they can find therein the means of extricating themselves from their disagreement; thus the assumed difference upon ideas ought not to serve as a pretext for eternal disputes, although I know that certain Cartesians, otherwise very able, are accustomed U> intrench themselves in the ideas which they pretend to have. But if they would avail themselves of the means which I have before given for recognizing ideas true and false, and of which we shall speak also in the sequel, they would retire from a position which is not tenable. Ph. The ideas, the perception of which comes to us from more than one sense, are those of space, or extension, or figure, of motion and rest. Tk. [The ideas which are said to come from more than one sense, like those of space, figure, motion, rest, are rather from common-sense, that is to say, from the mind itself, for they are ideas of the pure understanding, but related to externality, and which the senses make us perceive; they are also