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In Proposition 7, Part I of the Ethics Spinoza claims:

Existence belongs to the nature of substance.

This means that substance exists necessarily or, to put it even simpler, that each substance must be it's own cause (i.e. "causa sui" - see the proof of proposition 7). What do other philosophers think of this? I'm particularly interested in the views of Aristotle, Descartes and Medieval philosophers on the necessary existence of substance (or on the views of other philosophers who wouldn't accept Spinozas doctrine that substance exists necessarily). Is it a universally accepted doctrine or are there philosophers claiming that existence does in fact not belong to the nature of substance? If someone does, which consequences would follow from the rejection of Spinozas claim? Would it oblige them to grant the possiblity of non-existent substances? Or would any of them see substances not as themselves existing but only as something giving rise to existence? Or would any of them allow for one substance to bring another into existence? Or would they consider some substances as existing and others not? Or rather none of these consequences? It would be helpful if anyone could inform me on the issue.

Note: I know that Spinoza transforms the meaning of Substance profoundly in that he does conceive of substance in the singular, while the mentioned philosophers in general think about substances, i.e. in the plural, which means it is usually granted that there is a multiplicity of substances, while for Spinoza there is only one. Anyway, it would be nice if anyone could inform me on any position that rejects the view that substance (or substances if you will) exist(s) necessarily.

  • No, but it doesn't imply anything exciting. Contingent existence is not non-existence, and has no special consequences, it is the norm. Medieval philosophers admitted only one "necessary being", not substances generally. Aquinas explicitly separates existence as an act of being (esse) from any property in essence, or in accidence for that matter, they are not even of a kind. Except for God, and God alone, “esse essentia”, existence is essence. Btw, what "necessity" meant to Aquinas et al. has little to do with its modern meaning. – Conifold Feb 5 at 1:17
  • @Conifold thanks for your comment. Could you point me in any direction where I can inform myself about contingent existence/non-existence/necessary existence? – Moritz Wolff Feb 5 at 9:58
  • See SEP, Necessary Being and God and Other Necessary Beings. – Conifold Feb 5 at 12:03
  • You'll have to find this to make sure it's correct, but Aristotle claimed that 'primary ousia' [substance] is that 'which is the cause of everything yet present in nothing'. With a little juxta-positioning, this more or less equates with Spinoza's 'substance'. Look in Aristotle's 'Categories'. – Charles M Saunders Feb 5 at 12:43
  • See Aristotle's notion of substance: the answer is Yes and No. In Categories, individula substances are the basic subject of predication, and an individual "exists" is the usual sense. But in Met.Z A speaks of essence as substance, in which case things are different. – Mauro ALLEGRANZA Feb 5 at 16:02
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For Aristotle (4th century BC Greek philosopher) and St. Thomas Aquinas (13th century AD medieval philosopher/theologian), ‘substance’ is the primary category of being and is simply defined as an independent and contingently existing thing. As far as his treatment of existence is concerned, Aristotle does not develop an explicit viewpoint on this matter.

Aquinas develops the distinction between essence and existence in Chapter 4 of On Being and Essence. There, he notes that “one can have an understanding of what a man or a phoenix is without knowing whether it exists,” and so thus he considers existence to be an incidental property of being.

It should also be mentioned that earlier medieval scholars, such as 6th century AD philosopher Boethius, also take the distinction between esse and essentia to be self-evident. In Boethius' theological treatise entitled De hebdomadibus, one of his self-evident axioms is as follows: Diversum est esse et id quod est, or “what a thing is and that it is are not the same.”

As far as the consequences that would result from denying existence to be an essential property of substance, as Spinoza appears to have claimed, it would indeed oblige one to accept the possibility of so-called ‘non-existent substances’. This does not mean, however, that we must accept the odd conclusion that there actually exists substances which are non-existent. Since being can admit of both actuality and potentiality: the non-existence a substance has is only potentially so and with respect to something other than what it is actualized to be.

The reason is that being is “said in many ways” (Bk IV, Metaphysics, Aristotle), and one of the ways in which being is said is as it exists in a two-fold manner between actuality and potentiality (Bk IX, Metaphysics, Aristotle), and because substance and the other categories of being are the other ways in which being is said, substance can be both actually and potentially so--albeit in different respects. For instance, my mother may be actually a housewife and potentially a career-woman; what she cannot be is actually and potentially a housewife at the same time. Therefore, a substance can be non-existent but not in respect to itself but to what it is not and only potentially so.

Aquinas actually uses the terms ‘privation’ and ‘negation’ to refer to attributes which can be negated in thought but which posit nothing in reality, e.g. such as when someone is blind, or if there is blindness in the eye. Being blind refers to a particular quality which a person or an animal lacks (Chp. 4, On Being and Essence, Aquinas). To say of a substance that it does not exist is tantamount to signifying a truth of a proposition without referring to anything actually existing in reality.

As far as something not existing giving rise to something that does, Aristotle would have certainly taken exception. To the Greeks, the concept of generation ex nihilo is not a doctrine they agreed with. To my knowledge, Parmenides, a 6th century BC Greek philosopher, was one of the first to reject that notion, as quoted by Aristotle in his Physics. Aquinas also agrees with Aristotle on this point, viz. with respect to the emanation of particular effects from particular causes (A. 2, Q, 45, First Part of the Summa Theologiae, Aquinas)

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  • Methinks you have got Aritotles 'primary ousia' wrong. See my defintion above. – Charles M Saunders Sep 25 at 4:28

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