More familiar is the argument from design, an approach that penetrates deeply into issues of fundamental scientific concern. This argument was admirably summarized by David Hume: “Look round the world: contemplate the whole and every part of it; you will find it to be nothing but one great machine, subdivided into an infinite number of lesser machines.… All these various machines, even their most minute parts, are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them. The curious adapting of means to ends, throughout all nature, resembles exactly, though it much exceeds, the production of human contrivance; of human design, thought, wisdom, and intelligence. Since therefore the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble; and that the Author of Nature is somewhat similar to the mind of man; though possessed of much larger faculties proportioned to the grandure of the work which he has executed.

It has been generally, but not always, the custom of naturalists to degrade the powers of dumb animals into mere instinct, and not to allow them reason; and on the other hand to elevate the qualities of man, by entirely disavowing the power of instinct in man, giving him the use of reason alone. It appears to me, that there is such a quality as instinct; by which I understand a desire to do any thing without knowing why, or without having the object in view which it is to reach. I am of opinion that both reason and instinct act in man and also in brutes; and I will even grant that the proportion of reason to instinct is greater in man than in other animals; but that the latter possess a great portion of reason would it seems be absurd to dispute.

It has been said that man is a rational animal; while this formulation is insufficient and ill-sounding, it nonetheless points to an undeniable truth, though in an elliptical fashion, for the rational faculty actually serves to underscore the transcendence of man in relation to the animal. Man is rational because he possesses the Intellect, which by definition has a capacity for the absolute and therefore a sense of the relative; and he possesses the Intellect because he is made "in the image of God", which, moreover, he demonstrates physically by his corporeal form and his cranial form, as well as by his vertical posture, then by language and his productive capacity. Man is a theophany in his form as much as in his faculties.

[...] men are not astonish'd at the operations of their own reason, at the same time, that they admire the instinct of animals, and find a difficulty in explaining it, merely because it cannot be reduc'd to the very same principles. [...] reason is nothing but a wonderful and unintelligible instinct in our souls[.]

Human reason is by nature architectonic.

I think there is at least one moral theory of respectable lineage and good independent credentials that can accommodate such fairly minimal intuitions about us and animals. This is the theory Hume offers us. I do not consider Hume a forerunner of utilitarianism, and therefore what I shall go on to say in defense of Hume is not intended as a defense of any version of utilitarianism. I see Hume to be much closer to Aristotle than to Mill, to be offering us a theory about human virtues, not a theory about utility maximization and the duties that might involve.

Man is a rational animal, and if human affairs are hard to regulate, his twofold nature is usually the cause. Reason is something ultimate; it would be the same in another planet, or in another universe, as it is here. Animal nature is something contingent; it might have been different. Our life is a compromise, a blend between the animal and the rational.

Man is said to be a reasoning animal. I do not know why he has not been defined as an affective or feeling animal. Perhaps that which differentiates him from other animals is feeling rather than reason. More often I have seen a cat reason than laugh or weep. Perhaps it weeps or laughs inwardly — but then perhaps, also inwardly, the crab resolves equations of the second degree.

Reason in man is rather like God in the world.

Men have had the same origin as other animals; they have the same general architecture of body and mind; and they have the same destiny. And they stand on the same general level of ethical claim and obligation.

What we call human reason, is not the effort or ability of one, so much as it is the result of the reason of many, arising from lights mutually communicated, in consequence of discourse and writing.

The basis of the [scientific] method is a belief in natural uniformity – if two events are regularly connected in our observations we can conclude that they obey a universal law. But this is not a conclusion we reach by observation. No amount of evidence can demonstrate the existence of laws of nature, since new experience can always overturn them. Science rests on the belief that the future will be like the past; but that belief is rationally groundless. This is not a new line of thinking. David Hume argued that the expectation that the future will be like the past, which is the basis of induction, is a matter of habit. Hume wanted to show that since miracles transgress known laws of nature it was unreasonable to accept reports of them, in the Bible or anywhere else. But his arguments against induction showed that the laws of nature could not in fact be known, so events that seemed impossible could happen at any time. The upshot was that faith in miracles returned by the back door of sceptical doubt.

Animal is driven by instincts, human by values, aims and reasons.

Man is a rational animal. So at least we have been told. Throughout a long life I have searched diligently for evidence in favor of this statement. So far, I have not had the good fortune to come across it.