Now, speaking generally, this is the method of Scepticism, and it is most important. Because the sceptical conscience demonstrates that in all that is immediately accepted there is nothing secure and absolute, the Sceptics have taken in hand all particular determinations of the individual sciences, and have shown that they are not fixed. The further details of this application to the different sciences do not concern us here: this far-seeing power of abstraction is also requisite in order to recognize these determinations of negation or of opposition everywhere present in all concrete matter, and in all that is thought, and to find in this determinate its limits. Sextus, for example, takes up the individual sciences concretely, thereby demonstrating much capacity for abstraction, and he shows in all their determinations the opposite of themselves. Thus he sets the definitions of mathematics against one another, and that not externally, but as they are in themselves; he lays hold of the fact (adv. Math. III. 20-22) that there is said to be a point, space, line, surface, one, &c. We unquestioningly allow the point to rank as a simple unit in space, according to which it has no dimension; but if it has no dimension, it is not in space, and therefore is no longer a point. On the one hand it is the negation of space, and, on the other, inasmuch as it is the limit of space, it touches space. Thus this negation of space participates in space, itself occupies space, and thus it is in itself null, but at the same time it is also in itself a dialectic. Scepticism has thus also treated of ideas which are, properly speaking, speculative, and demonstrated their importance; for the demonstration of the contradiction in the finite is an essential point in the speculatively philosophic method.