P11: God/Nature, or a substance consisting of infinite attributes, each of which expresses eternal and infinite essence, necessarily exists.

Dem.: If you deny this, conceive, if you can, that God/Nature does not exist. Therefore (by A7) his essence does not involve existence. But this (by P7) is absurd. Therefore God/Nature necessarily exists, q.e.d.

Alternatively: For each thing there must be assigned a cause, or reason, as much for its existence as for its nonexistence. For example, if a triangle exists, there must be a reason or cause why it exists; but if it does not exist, there must also be a reason or cause which prevents it from existing, or which takes its existence away. But this reason, or cause, must either be contained in the nature of the thing, or be outside it. E.g., the very nature of a square circle indicates the reason why it does not exist, viz. because it involves a contradiction. On the other hand, the reason why a substance exists also follows from its nature alone, because it involves existence (see P7). But the reason why a circle or triangle exists, or why it does not exist, does not follow from the nature of these things, but from the order of the whole of corporeal Nature. For from this {order} it must follow either that the triangle necessarily exists now or that it is impossible for it to exist now. These things are evident through themselves, but from them it follows that a thing necessarily exists if there is no reason or cause which prevents it from existing. Therefore, if there is no reason or cause which prevents God/Nature from existing, or which takes his existence away, it must certainly be inferred that he necessarily exists.

But if there were such a reason, or cause, it would have to be either in God/Nature’s very nature or outside it, i.e., in another substance of another nature. For if it were of the same nature, that very supposition would concede that God/Nature exists. But a substance which was of another nature {NS: than the divine} would have nothing in common with God/Nature (by P2), and therefore could neither give him existence nor take it away. Since, then, there can be, outside the divine nature, no reason, or, cause which takes away the divine existence, the reason will necessarily have to be in his nature itself, if indeed he does not exist. That is, his nature would involve a contradiction {NS: as in our second Example}. But it is absurd to affirm this of a Being absolutely infinite and supremely perfect. Therefore, there is no cause, or reason, either in God/Nature or outside God/Nature, which takes his existence away. And therefore, God/Nature necessarily exists, q.e.d.

Alternatively: To be able not to exist is to lack power, and conversely, to be able to exist is to have power (as is known through itself). So, if what now necessarily exists are only finite beings, then finite beings are more powerful than an absolutely infinite Being. But this, as is known through itself, is absurd. So, either nothing exists or an absolutely infinite Being also exists. But we exist, either in ourselves, or in something else, which necessarily exists (see A1 and P7). Therefore an absolutely infinite Being—i.e. (by D6), God/Nature—necessarily exists, q.e.d.

Schol.: In this last demonstration I wanted to show God/Nature’s existence a posteriori, so that the demonstration would be perceived more easily—but not because God/Nature’s existence does not follow a priori from the same foundation. For since being able to exist is power, it follows that the more reality belongs to the nature of a thing, the more powers it has, of itself, to exist. Therefore, an absolutely infinite Being, or God/Nature, has, of himself, an absolutely infinite power of existing. For that reason, he exists absolutely.

Still, there may be many who will not easily be able to see how evident this demonstration is, because they have been accustomed to contemplate only those things that flow from external causes. And of these, they see that those which quickly come to be, i.e., which easily exist, also easily perish. And conversely, they judge that those things to which they conceive more things to pertain are more difficult to do, i.e., that they do not exist so easily. But to free them from these prejudices, I have no need to show here in what manner this proposition—what quickly comes to be, quickly perishes—is true, nor whether or not all things are equally easy in respect to the whole of Nature. It is sufficient to note only this, that I am not here speaking of things that come to be from external causes, but only of substances that (by P6) can be produced by no external cause. For things that come to be from external causes—whether they consist of many parts or of few—owe all the perfection or reality they have to the power of the external cause; and therefore their existence arises only from the perfection of their external cause, and not from their own perfection. On the other hand, whatever perfection substance has is not owed to any external cause. So its existence must follow from its nature alone; hence its existence is nothing but its essence. Perfection, therefore, does not take away the existence of a thing, but on the contrary asserts it. But imperfection takes it away. So there is nothing of whose existence we can be more certain than we are of the existence of an absolutely infinite, or perfect, Being—i.e., God/Nature. For since his essence excludes all imperfection, and involves absolute perfection, by that very fact it takes away every cause of doubting his existence, and gives the greatest certainty concerning it. I believe this will be clear even to those who are only moderately attentive.