substance

is an entity which needs no other entity in order to exist (i.e. God, mind, and matter).

Descartes means by 'substance' an entity which exist in such a way that it needs no other entity in order to exist. Therefore, only God is a substance in this strict sense. But he extends the term to created things, which need only the concurrence of God to exist. Of these there are two and only two: mind and matter, (wiki)

is something which does not require the concept of another thing from which it must be formed.

By substance I understand what is in itself and is conceived through itself, i.e., that whose concept does not require the concept of another thing, from which it must be formed.(E1D3)

To give two Kantian examples, the category 'substance' is the 'permanence of the real in time' and the category 'cause' is 'succession subject to a rule' (Dostal in Guignon: 145)

is a term referring to the very structure of existence, underlying all events and things, and constituting the essence of the world.

If now we compare this division of the world into substance and modes with its division, in The Improvement of the Intellect, into the eternal order of laws and invariable relations on the one hand, and the temporal order of time-begotten and death-destined things on the other, we are impelled to the conclusion that Spinoza means by substance here very nearly what he meant by the eternal order there. Let us provisionally take it as one element in the term substance, then, that it betokens the very structure of existence, underlying all events and things, and constituting the essence of the world.

is “that which is", the present participle of einai; to be; that which eternally and unchangeably is, and of which everything else must be a transient form or mode.

If we go back to the Scholastic philosophers from whom Spinoza took the term, we find that they used it as a translation of the Greek ousia, which is the present participle of einai; to be, and indicates the inner being or essence. Substance then is that which is (Spinoza had not forgotten the impressive "I am who am" of Genesis) ; that which eternally and unchangeably is, and of which everything else must be a transient form or mode.

is not easy to come by --- It is easier to speak than to say something.

It is easier to speak than to say something.

That substance is insubstantial, that it is form and not matter, that it has nothing to do with that mongrel and neuter composite of matter and thought which some interpreters have supposed it to be, stands out clearly enough from this identification of substance with creative but not with passive or material nature. A passage from Spinoza's correspondence may help us:

is, ironically, insubstantial and creative, having nothing to do with that mongrel and neuter to do with that mongrel and neuter composite of matter and thought which some interpreters have supposed it to be.

substance, n.Definitions

substance