Eo ipso means "by (or from) the thing itself" in Latin and is similar to the sense expressed by the English idioms, "by the same token", "of itself", or "on its own account". It is often used in various schools of philosophy to demonstrate the possibility/impossibility of propositions from their nature. For example: "That I am does not eo ipso mean that I think." The term is also used in law, and it is through law that it was brought into English from Latin.
In The Crisis and a Crisis in the Life of an Actress, Søren Kierkegaard describes the quality of eo ipso:
But to be gallant towards an artist is precisely the highest degree of insolence, a maudlin impertinence and a disgusting kind of intrusiveness. Anyone who is something, and is something essentially, possesses "eo ipso," the claim to be recognized for exactly this special thing, and for nothing more or less.
Also see the following aphorism from Nietzsche's Beyond Good and Evil (p. 73), as translated by Walter Kaufmann (1966): "Whoever reaches his ideal transcends it eo ipso."
- Kierkegaard, Søren. The Crisis and a Crisis in the Life of an Actress, Harper & Row, 1967, p. 69.
The dictionary definition of 'eo ipso' at Wiktionary