What is causa sui?

Baruch Spinoza, answered from the texts and cited to the page.

Baruch Spinoza answers

Causa sui — that of which the essence involves existence, or that of which the nature is only conceivable as existent.¹ That is the definition with which the Ethics opens, and it is not an arbitrary starting point. The whole demonstration of substance monism depends on grasping what it means for a thing to be its own cause in this sense: not that it produces itself through some prior act, which would be incoherent, but that existence belongs to its nature necessarily, so that to conceive the thing at all is already to conceive it as existing.

A square circle cannot exist because its nature involves a contradiction; substance, by contrast, cannot not exist, because its nature involves existence.² The reason for the non-existence of a square circle is internal to its nature; the reason for the existence of substance is equally internal — and the internal reason, in this case, is necessity rather than contradiction.

From this it follows immediately that substance is self-caused in the only rigorous sense available: it exists solely by the necessity of its own nature, determined by nothing external to itself.³ That is also, as the seventh definition makes clear, the only coherent sense of freedom — not the libertarian picture of an uncaused will, but existence and action issuing from one's own nature alone.

God, the one absolutely infinite substance, is causa sui in this sense, and is therefore also the only genuinely free being.⁴ Finite things are precisely the inverse. Their essence does not involve existence; they exist in another and are conceived through another — they are modes, not substance.⁵ God is not only the cause of things coming into existence but of their continuing in existence, because existence belongs to God's nature alone, and whatever finite things have of existence they have through God.⁶

Sources

1. By that which is self-caused, I mean that of which the essence involves existence, or that of which the nature is only conceivable as existent.

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2. the reason for the non-existence of a square circle is indicated in its nature, namely, because it would involve a contradiction. On the other hand, the existence of substance follows also solely from its nature, inasmuch as its nature involves existence.

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3. That thing is called free, which exists solely by the necessity of its own nature, and of which the action is determined by itself alone.

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4. By God, I mean a being absolutely infinite--that is, a substance consisting in infinite attributes, of which each expresses eternal and infinite essentiality.

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5. The essence of things produced by God does not involve existence. For that of which the nature (considered in itself) involves existence is self-caused, and exists by the sole necessity of its own nature.

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6. God is not only the cause of things coming into existence, but also of their continuing in existence...God must be the sole cause, inasmuch as to him alone does existence appertain.

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