One of Descartes' proofs of God's existence is that we can think of a perfect being, while being imperfect, so the perfect being has to have implanted the idea of Him in us and thus is real. But I can also think of a unicorn that is perfect, that's even more simple for me than to think of a perfect God.

Does this mean that God and the unicorn are the same? Or that God is just not the only perfect being (wouldn't that make him less perfect?) or that I just falsely interpret the unicorn to be perfect?

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  • The "assumption" of Descartes' proof is that the concept of God needs (it necessarily implies) the "property" of existence, i.e. when we think at God we are necessarily "forced" by the same concept to include existence among its intrinsec properties. This is not true for the concept dog nor for the concept unicorn, period. The "assumption" is very very debatable... but it is what it is. Jan 4, 2017 at 18:04
  • Descartes was trying to reconcile his propensity for belief with his dedication to reason. Pascal suffered the same flaw with his 'wager'. Remember, Descartes is best known for his "I think, therefore I am" quote which reeks of the subjective. A more accurate way to state it is "I am, and I think, therefore I can reason that I exist." You can't make any assertion about anything existent without first acknowledging the axiom that existence exists.
    – Scott
    Jan 4, 2017 at 21:09
  • You will have to define what 'perfect' is according to your viewpoint. If 'perfect' stands for omnipotent, omnipresent, and all-good it turns out we can't actually imagine all them together without creating a conflict and/or it does not fit our observations. Jan 5, 2017 at 23:36

4 Answers 4


Descartes actually addresses something quite close to your objection.

In Meditation 3 where Descartes makes this argument, he suggests that ideas can have three sources:

  1. innate - we are born with
  2. adventitious - come to us from outside (as for example our senses).
  3. imagined - made by fusing different ideas together

Descartes deals specifically at one point with how we can handle animals that we have never seen. His answer is that we do so by taking adventitious ideas and mixing them together. In the case of a unicorn, we are mixing the idea of a horse with some other ideas we've got like horns.

In your question, you suggest, couldn't we have a perfect unicorn. To answer this, we need to think about what perfect means. In your question, I am not entirely sure I grasp its meaning, but I can imagine you mean one of two things:

  • Perfect-1 = most desirable to me.
  • Perfect-2 = best thing.

Perfect-1 isn't much of a useful criterion and does not at all seem to be what Descartes has in mind. Perfect-2 appears more useful as a criterion, but it fails to do any good work, because we just punt from "perfect" to "best".

Descartes has something else in mind by perfect than either of these in his "idea of perfection." He means roughly an idea that is unlimited and has what we call "all the perfections." But we actually don't need to completely solve what it is.

We can return to the three types of ideas that Descartes thinks we can have and how we can use these to understand things. Descartes suggests that we understand like this:

  • God from the idea of perfection
  • Angels from mixing our idea of God and our idea of ourselves
  • Humans from our experience of ourselves
  • Ourselves from our experience of ourselves
  • Animals from our experience of ourselves and our experience of things
  • Things from our experience of things

For all of these except God, Descartes thinks we can explain them by what we experience regularly. And that all of them are things we receive in flawed and imperfect ways. (This argument may seem quite dubious to us, but Descartes is less a pure product of modern foundationalism and more a product of medieval scholasticism).

What Descartes finds impressive and uses a proof for God is a type of cosmological proof built on the existence in him of an idea of perfection. This idea stands in contrast to the ideas of himself and animals and things that he can get from experience. First, it contrasts with them in that these ideas are all received imperfectly from the dubious senses. Second, it contrasts with them in having no flaws or gaps in terms of its object. I can have mistaken ideas about cows or myself (see Med. 1 and 2), but I can't on his view have a mistaken idea of perfection itself.

From this, he argues that this idea cannot have come from anything but perfection itself, ergo perfection itself exists.

Why can't this be the unicorn? Well, unicorns are pretty limited things. We see them as occupying a particular place and time and being, well, roughly like horses but different. And that means we can easily see how we combine several adventitious ideas. Descartes's specific example is a chimera (if memory serves) and how it mixes lion and another animal. The same would work here.

  • Here is my issue. When Anselm proposed his ontological argument Gaunilon objected that the same type of reasoning leads to existence of a perfect island. That islands or unicorns are limited and adventitious is beside the point, and so is the nature of perfection, as long as we accept that existing X is "more perfect" than non-existing X. With that, and the idea that perfect X is conceivable, we get existence of all perfect X's along with Anselm's God, unless there is a special pleading for the summum bonum. But then, like cogito, it is not an argument but an appeal to intellectual ostension.
    – Conifold
    Jan 5, 2017 at 21:58
  • I'm not following. Anselm provides an ontological argument (or at least that's how it's been interpreted). Descartes is provided a cosmological argument that has to do with his individual self having this notion. The idea of a unicorn is clearly like the chimera: horse + horns. There's no degrees of perfection at work as there was in Anselm's. / A better angle of attack vs. Descartes is to argue that many people do not in fact have the idea of perfection -- which would undermine it or that it can be achieved from a sum of imperfect sources (contra his claim).
    – virmaior
    Jan 5, 2017 at 22:40
  • Kant and SEP apparently interpret Descartes' argument as ontological, but I am not sure if it is best interpreted as an argument at all. There seems to be, as with cogito, an irresistible appeal in it, "there got to be something there", which drove many first class thinkers to try to fix its apparent logical flaws. If pointing at an object we expect others to see, and saying "there is X over there" is converted into an argument, in form it will be a fallacy. But in this case we feel it must follow, cf. Kant's "sole fact of reason".
    – Conifold
    Jan 5, 2017 at 23:17

The unicorn would be less perfect, being limited, for instance to having four feet, which is not always the perfect number. Say I want to kick seven people simultaneously. Then, for the instant of that whim, seven feet would be a better number to have. In the sense Descartes is using perfect perfection is always and everywhere perfect and is not situational.

That means there can be at most one perfect being.

Two perfect beings, neither of which had any advantage over the other in any circumstance would necessarily be two identical instances of a single being. Both would have to be everywhere equally, both would have to have the same ability and the same effect in all circumstances, etc. There would be no way to tell them apart. Nor would there be any point in both of them serving any given end, as either would already suffice.

And yet the perfect being would not be annoyingly contrary to Occam's razor in being pointlessly double. Were it double, it would be so to some effect.


Here in the Meditations, Descartes is essentially referring to a well-known theological argument that has a long history in philosophy before him. It is perhaps most easily understood as originally formulated by the ancient Greek philosopher Plato and his later followers, who conceived of what we would call God as the "unity of all perfections," a simple singularity which is all good, all beautiful, all wise, eternal, incorruptible, and in all other ways perfect. A good way to picture this is as an infinitely bright point source of light orbited by increasingly imperfect copies of itself. The reason for its necessary existence is that it can be the "parent" of the corrupted things, but not their "child," because the copying process degrades rather than purifies.

Thus, everything else that exists, in this conception, is a corrupted copy of the One, and the complexities of existing things are a part of the corruption. The unicorn is distinguishable from the One by virtue of its identifiably non-perfect characteristics. We can conceive of something more perfect than it, therefore it is not God.

There are some challenges in reconciling this conception with the core Christian concept of the Incarnation, but those are not relevant to the argument Descartes uses here, which does not rely on a personified conception of God.

  • Descartes was Catholic, so where do you get the idea that his concept of God was neoplatonic?
    – user3017
    Jan 5, 2017 at 13:08
  • If you read the Meditations themselves, that is the portrait of God painted there. As it turns out, there's quite a strong neoplatonic lineage in Catholic theology, straight through from Saint Augustine. This would have been quite familiar to Descartes through his scholastic education. In addition, while Descartes definitely was Catholic, his religious and scientific beliefs are demonstrably not in line with the orthodoxy of his time --there are clear records showing he worried that his writings would bring him into conflict with the church. Jan 5, 2017 at 13:59
  • I've seen argument to that effect, but I've never seen any good evidence. In fact, the inability of anyone to find good evidence suggests that it doesn't exists, and I've found many of the arguments to be embarrassingly presumptuous. I believe you're mistaken about Augustine as well. He criticized many of Plato's beliefs. Instead of believing everything you read, you might try to find evidence in the writings of Descartes and Augustine themselves before spreading hollow accusations.
    – user3017
    Jan 5, 2017 at 14:11
  • "It was, nevertheless, quite a new spirit which informed [Augustine's] declarations, the spirit of a pure theism, derived, not from his philosophical predecessors, but from those Scriptures which themselves also told him of the true light that lighteth every man who cometh into the world." B. B. Warfield
    – user3017
    Jan 5, 2017 at 14:22
  • I think the work on Plotinus and by Plotinus scholars shows a pretty clear link between Neoplatonism (at least as the term is used in philosophy) and Augustine. If you doubt it, see plato.stanford.edu/entries/augustine , protevi.com/john/SH/PDF/Neoplatonism.pdf , individual.utoronto.ca/pking/articles/…
    – virmaior
    Jan 5, 2017 at 14:36

In your question you use the term "perfect" in two different ways: as a property of God, and as a property of the unicorn. If God and the unicorn were perfect in exactly the same way then they would be the same (assuming the definition of "perfect" in question allows for the existence of only one perfect thing, much like the maximal element in a fully ordered set). However, the "perfectness" of the unicorn is understood to be bound to the form of the unicorn itself, as imagined by the observer in question. Thus, the answer to all your questions but the second is no.

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