Does Spinoza think essence and eternity are the same thing?

Question

"VIII. By eternity, I mean existence itself, in so far as it is conceived necessarily to follow solely from the definition of that which is eternal."

"Explanation—Existence of this kind is conceived as an eternal truth, like the essence of a thing, and, therefore, cannot be explained by means of continuance or time, though continuance may be conceived without a beginning or end." -- Ethics, Part I. Concerning God

Spinoza says that eternity or eternal can’t be defined by time/continuance. He says eternal/eternity implies essence. Hence, is essence the definition of eternity and vice versa according to Spinoza?

Answer 1

Ethics Part 1- Definition 7- "By eternity, I mean existence itself, in so far as it is conceived to follow solely from the definition of that which is eternal." Explanation- "Existence of this kind is conceived as an eternal truth, like the essence of a thing, and, therefore, cannot be explained by means of continuance or time, though continuance may be conceived without a beginning or end."

The answer is absolutely yes. Spinoza's definitions must be understood on his terms and present day definitions do not hold. The relationship among existence, essence and eternity is 'dynamic'. They effectively fold into one another and form one completely undifferentiated complete 'unity'. For the most accurate interpretation of Spinoza's philosophy see, Harold Foster Hallett, "Spinoza- the Elements of his Philosophy". It is not an easy read but remains the best. Good luck!

Answer 2

No, except if you are willing to apply some twists to his writings. From late antiquity scholastics adopted a distinction between "perpetuity" and "eternity"; much has been written on the topic but there are good introductions to the topic e.g. Siniossoglou (2005) Time, Perpetuity and Eternity in Late Antique Platonism. Roughly put "eternal" is what exists somehow outside of infinite time, which is called perpetuity: e.g. truths of logic or arithmetic were taken to be eternal.

Ethics Part.I, Def.4 states “Per attributum intelligo id, quod intellectus de substantia percipit, tanquam ejusdem essentiam constituens. and there is a SEP article about attributes according to Spinoza. Ultimately "deus sive natura" is eternal and allows to conceive eternity.