The English language phrases Ipso Facto and De Facto have related meanings, but they are different as I shall explain, with examples of their British English usage.
Ipso Facto means "by the fact itself" - i.e. something that is immediately known from an initial fact.
"I am English, ipso facto British". This is because all English people are British.
"Faustus had signed his life away, and was, ipso facto, incapable of repentance."
De Facto means "something that exists in reality, but not officially recognized by law".
"English is the de facto language of Great Britain." There is no law that says English is the official language of the UK, but everyone knows it is.
"She is my de facto wife, even though we have not been married." In Australia and New Zealand, people who live together as husband and wife are treated as if they are married, even though they are not.
Please note that neither phrase is commonly used in British English language outside of some academic or legal communities.
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