"There is yet one other Idea which I shall mention, though it is one about which difficulties have been raised, since the consideration of such difficulties may be instructive: the Idea of a purpose, or as it is often termed, a _Final Cause_, in organized bodies. It has been held, and rightly, that the assumption of a Final Cause of each part of animals and plants is as inevitable as the assumption of an efficient cause of every event. The maxim, that in organized bodies nothing is _in vain_, is as necessarily true as the maxim that nothing happens _by chance_. I have elsewhere shown fully that this Idea is not deduced from any special facts, but is assumed as a law governing all facts in organic nature, directing the researches and interpreting the observations of physiologists. I have also remarked that it is not at variance with that other law, that plants and that animals are constructed upon general plans, of which plans, it may be, we do not see the necessity, though we see how wide is their generality. This Idea of a purpose,--of a Final Cause,--then, thus supplied by our minds, is found to be applicable throughout the organic world. It is in virtue of this Idea that we conceive animals and plants as subject to _disease_; for disease takes place when the parts do not fully answer their _purpose_; when they do not do what they _ought_ to do. How is it then that we thus find an Idea which is _supplied_ by our own minds, but which is _exemplified_ in every part of the organic world? Here perhaps the answer will be readily allowed. It is because this Idea is an Idea of the Divine Mind. There _is_ a Final Cause in the constitution of these parts of the universe, and therefore we can interpret them by means of the Idea of Final Cause. We can _see_ a purpose, because there _is_ a purpose. Is it too presumptuous to suppose that we can thus enter into the Ends and Purposes of the Divine Mind? We willingly grant and declare that it would be presumptuous to suppose that we can enter into them to any but a very small degree. They doubtless go immeasurably beyond our mode of understanding or conceiving them. But to a certain extent we _can_ go. We can go so far as to see that they _are_ Ends and Purposes. It is _not_ a vain presumption in us to suppose that we know that the eye was made for seeing and the ear for hearing. In this the most pious of men see nothing impious: the most cautious philosophers see nothing rash. And that we can see thus far into the designs of the Divine Mind, arises, we hold, from this:--that we have an Idea of Design and of Purpose which, so far as it is merely _that_, is true; and so far, is Design and Purpose in the same sense in the one case and in the other."[81] * * * * *