Aquinas starts from first principles, discussing how things differ from inanimate objects and forces, to plants, to animals. His point will offend the hard vegans: it is that there are different natures for different things. It is worthwhile consider that humans are in the middle: we are animals, but sentient, and have some spiritual sensitivity.
1 As starting point for this intention, one must take this: Following a diversity of natures, one finds a diverse manner of emanation in things, and, the higher a nature is, the more intimate to the nature is that which flows from it.
2 For, in all things, inanimate bodies have the lowest place. There can be no emanations in these except by the action of some one upon another one. For this is the way in which fire is generated by fire, when an extraneous body is changed by the fire and is brought to the quality and species of fire.
3 Among animate bodies the next place is held by the plants, and in these the emanation does proceed somewhat from what is within: to the extent, namely, that the internal humor of the plant is converted into seed and that the seed committed to the soil grows into a plant. Here, then, one has already found the first grade of life, for living things are those which move themselves to action, but those which can move only things external to them are entirely devoid of life. And in plants this is the mark of life: that which is within, them moves toward some form.
The life of plants is nevertheless imperfect; this is because, although the emanation in plants proceeds from what is within, what comes forth little by little in the emanation is, at the end, found to be entirely external. For the humor first emerging from the tree becomes a blossom, and at length a fruit distinct from the tree’s bark, yet still fastened to it. But, when the fruit is perfected, it is separated from the tree altogether; it falls to the ground and its seeding power produces another plant. If one also considers this carefully, he will see that originally this emanation comes from what is external, for the internal humor of the tree is taken through the roots from the soil from which the plant receives nourishment.
4 Beyond the life of plants one finds a higher grade of life: that of the sensitive soul. Its emanation may have an external beginning, but has an internal termination, and, the more fully the emanation proceeds, the more it reaches what is within. For the exterior sensible impresses its form on the exterior senses; from these it proceeds to the imagination and, further, to the storehouse of the memory. Nevertheless, in each step of this emanation the principle and the term refer to different things; no sensitive power reflects upon itself. This grade of life, then, is higher than the life of plants—higher to the extent that its operation takes place within the principles which are within; it is, nevertheless, not an entirely perfect life, since the emanation is always from some first to some second.
5 That, then, is the supreme and perfect grade of life which is in the intellect, for the intellect reflects upon itself and the intellect can understand itself. But even in the intellectual life one finds diverse grades. For the human intellect, although it can know itself, does indeed take the first beginning of its knowledge from without, because it cannot understand without a phantasm, as is clear from the things said before.
There is, therefore, a more perfect intellectual life in the angels. In them the intellect does not proceed to self-knowledge from anything exterior, but knows itself through itself. Nonetheless, it is not the ultimate perfection to which their life belongs. The reason is this: Although the intention understood is entirely intrinsic to them, the very intention understood is not their substance, for in them understanding is not identified with being (as is clear from the foregoing). Therefore, the ultimate perfection of life belongs to God, in whom understanding is not other than being, as has been shown; accordingly, the intention understood in God must be the divine essence itself.
Calvin is also working from first principles, but he is a more practical and interested in the human, not the angelic condition. Or the condition of one's dog.
1. It was not without reason that the ancient proverb so strongly recommended to man the knowledge of himself. For if it is deemed disgraceful to be ignorant of things pertaining to the business of life, much more disgraceful is self-ignorance, in consequence of which we miserably deceive ourselves in matters of the highest moment, and so walk blindfold. But the more useful the precept is, the more careful we must be not to use it preposterously, as we see certain philosophers have done. For they, when exhorting man to know himself, state the motive to be, that he may not be ignorant of his own excellence and dignity. They wish him to see nothing in himself but what will fill him with vain confidence, and inflate him with pride. But self-knowledge consists in this, first, When reflecting on what God gave us at our creation, and still continues graciously to give, we perceive how great the excellence of our nature would have been had its integrity remained, and, at the same time, remember that we have nothing of our own, but depend entirely on God, from whom we hold at pleasure whatever he has seen it meet to bestow; secondly, When viewing our miserable condition since Adam’s fall, all confidence and boasting are overthrown, we blush for shame, and feel truly humble. For as God at first formed us in his own image, that he might elevate our minds to the pursuit of virtue, and the contemplation of eternal life, so to prevent us from heartlessly burying those noble qualities which distinguish us from the lower animals, it is of importance to know that we were endued with reason and intelligence, in order that we might cultivate a holy and honourable life, and regard a blessed immortality as our destined aim. At the same time, it is impossible to think of our primeval dignity without being immediately reminded of the sad spectacle of our ignominy and corruption, ever since we fell from our original in the person of our first parent. In this way, we feel dissatisfied with ourselves, and become truly humble, while we are inflamed with new desires to seek after God, in whom each may regain those good qualities of which all are found to be utterly destitute.
2. In examining ourselves, the search which divine truth enjoins, and the knowledge which it demands, are such as may indispose us to every thing like confidence in our own powers, leave us devoid of all means of boasting, and so incline us to submission. This is the course which we must follow, if we would attain to the true goal, both in speculation and practice. I am not unaware how much more plausible the view is, which invites us rather to ponder on our good qualities, than to contemplate what must overwhelm us with shame—our miserable destitution and ignominy. There is nothing more acceptable to the human mind than flattery, and, accordingly, when told that its endowments are of a high order, it is apt to be excessively credulous. Hence it is not strange that the greater part of mankind have erred so egregiously in this matter. Owing to the innate self-love by which all are blinded, we most willingly persuade ourselves that we do not possess a single quality which is deserving of hatred; and hence, independent of any countenance from without, general credit is given to the very foolish idea, that man is perfectly sufficient of himself for all the purposes of a good and happy life. If any are disposed to think more modestly, and concede somewhat to God, that they may not seem to arrogate every thing as their own, still, in making the division, they apportion matters so, that the chief ground of confidence and boasting always remains with themselves. Then, if a discourse is pronounced which flatters the pride spontaneously springing up in man’s inmost heart, nothing seems more delightful. Accordingly, in every age, he who is most forward in extolling the excellence of human nature, is received with the loudest applause. But be this heralding of human excellence what it may, by teaching man to rest in himself, it does nothing more than fascinate by its sweetness, and, at the same time, so delude as to drown in perdition all who assent to it. For what avails it to proceed in vain confidence, to deliberate, resolve, plan, and attempt what we deem pertinent to the purpose, and, at the very outset, prove deficient and destitute both of sound intelligence and true virtue, though we still confidently persist till we rush headlong on destruction? But this is the best that can happen to those who put confidence in their own powers. Whosoever, therefore, gives heed to those teachers, who merely employ us in contemplating our good qualities, so far from making progress in self-knowledge, will be plunged into the most pernicious ignorance.
In this postmodern age, the idea that we are completely rational is obviously wrong. We see too many people being irrational most days. It is better to say what we don't know, and the more I know, the more deep my understanding of just how ignorant I truly am.