The manifest adaptation of each animal for its mode of life and outward means of subsistence, even down to the smallest detail, together with the exceeding perfection of its organisation, form abundant material for teleological contemplation, which has always been a favourite occupation of the human mind, and which, extended even to inanimate Nature, has become the argument of the Physico-theological Proof. The universal fitness for their ends, the obviously intentional design in all the parts of the organism of the lower animals without exception, proclaim too distinctly for it ever to have been seriously questioned, that here no forces of Nature acting by chance and without plan have been at work, but a will. Now, that a will should act otherwise than under the guidance of knowledge was inconceivable, according to empirical science and views. For, up to my time, as has been shown in the last chapter, _will_ and _intellect_ had been regarded as absolutely inseparable, nay, the will was looked upon as a mere operation of the intellect, that presumptive basis of all that is spiritual. Accordingly wherever the will acted, knowledge must have been its guide; consequently it must have been its guide here also. But the mediation of knowledge, which, as such, is exclusively directed towards the outside, brings with it, that a will acting by means of it, can only act outwardly, that is, only from _one_ being upon _another_. Therefore the will, of which unmistakable traces had been found, was not sought for where these were discovered, but was removed to the outside, and the animal became the product of a will foreign to it, guided by knowledge, which must have been very clear knowledge indeed, nay, the deeply excogitated conception of a purpose; and this purpose must have preceded the animal's existence, and, together with the will, whose product the animal is, have lain outside that animal. According to this, the animal would have existed in representation before existing in reality. This is the basis of the train of thought on which the Physico-theological Proof is founded. But this proof is no mere scholastic sophism, like the Ontological Proof: nor does it contain an untiring natural opponent within itself, like the Cosmological Proof, in that very same law of causality to which it owes its existence. On the contrary, it is, in reality, for the educated, what the Keraunological Proof[217] is for the vulgar,[218] and its plausibility is so great, so potent, that the most eminent and at the same time least prejudiced minds have been deeply entangled in it. Voltaire, for instance, who, after all sorts of other doubts, always comes back to it, sees no possibility of getting over it and even places its evidence almost on a level with that of a mathematical demonstration. Even Priestley too declares it to be irrefutable.[219] Hume's reflection and acumen alone stood the test, even in this case; in his "Dialogues on Natural Religion,"[220] which