In other parts of the external economy, invariability in all primary aspects is found compatible with modifications in points of secondary importance. These modifications become more numerous and extensive as the phenomena are more complex. The reason of this is that the causes from a combination of which the effects proceed being more varied and more accessible, offer greater facilities to our feeble powers to interfere with advantage. But all this has been fully explained in my _System of Positive Philosophy_. The tendency of that work was to show that our intervention became more efficacious in proportion as the phenomena upon which we acted had a closer relation to the life of man or society. Indeed the extensive modifications of which society admits, go far to keep up the common mistake that social phenomena are not subject to any constant law. At the same time we have to remember that this increased possibility of human intervention in certain parts of the External Order necessarily coexists with increased imperfection, for which it is a valuable but very inadequate compensation. Both features alike result from the increase of complexity. Even the laws of the Solar System are very far from perfect, notwithstanding their greater simplicity, which indeed makes their defects more perceptible. The existence of these defects should be taken into careful consideration; not indeed with the hope of amending them, but as a check upon unreasoning admiration. Besides, they lead us to a clearer conception of the true position of Humanity, a position of which the most striking feature is the necessity of struggling against difficulties of every kind. Lastly, by observing these defects we are less likely to waste our time in seeking for absolute perfection, and so neglecting the wiser course of looking for such improvements as are really possible.