The improvement in our nature may be physical, intellectual, or moral. The first would consist in an addition to the average duration of human life; it depends upon the progress of biology, and, consequently, of medicine and hygiene. Intellectual (scientific and æsthetic) improvement, would be still more desirable. It “means a greater soaring upwards” than is represented by all physical improvements or _a fortiori_ by any material improvements: for the intellect is a “universal tool” whose uses have a universal application. But human happiness depends far more upon moral progress “over which we have, also more command, although it is more difficult.” No intellectual improvement could be equal in value to an increase in goodness or in courage. If we were wise our whole endeavour therefore would be in this direction. At any rate we ought always to remember that other forms of progress are desirable simply as means, and moral progress alone as an end.[273] III. The theory of progress is the “principle” of social dynamics, itself the essential part of sociology, while sociology lies at the heart of positive philosophy. It was therefore to be expected that the adversaries of this philosophy would especially seek to ruin the theory of progress, which supports everything else. Indeed the objections have been numerous and pressing. Of these objections Comte had foreseen the two most important, and he had endeavoured to answer them beforehand. According to him, the theory of progress implies neither fatalism nor optimism, nor the quietism which has been represented as a consequence of it.[274] On the first point, Comte draws our attention to the fact that the necessary consequence of his principle of laws is not the absolute determinism of phenomena, whether it be a question of social or other phenomena. Positive philosophy admits nothing absolute. Determinism, like free-will, is a metaphysical thesis, Comte is not compelled to take sides either with one or the other: he leaves them to mutually refute each other. The positive conception of the moral and intellectual faculties of man, as Gall clearly established, does not imply that human actions might not be otherwise than they are. Similarly, if in general natural phenomena are subject to laws, this does not prevent us from conceiving these phenomena as modifiable by man’s intervention. Now, of all natural phenomena, social phenomena are precisely the most modifiable; so much so that for a long time it was possible to ignore that they were governed by laws.