Ipso facto is Latin for itself fact. In English, we use it as an adverb meaning by that very fact. It’s usually used where a necessary conclusion can be derived from one fact even where other facts would contribute to the conclusion. For example, we might say that while there are several reasons ipso facto is useful, the fact that there is no one-word English equivalent makes it ipso facto a welcome addition to the language.
Ipso facto is usually postpositive, meaning it follows the word it modifies. But this is not a rule, and the phrase does sometimes come before what it modifies—so “the fact that there is no one-word English equivalent makes it ipso facto a welcome addition” could instead be “the fact that there is no one-word English equivalent ipso facto makes it a welcome addition” (ipso facto here modifies the verb makes).
There is no need to italicize ipso facto in normal use (it is italicized in this post because it’s a phrase presented out of context). It has been in English for several centuries and is fairly common, and loanwords usually lose the italics once they’re well established in the language. Ipso facto passed that point long ago.
Prince Charles, heir to the British throne and – ipso facto – defender-in-waiting of the Anglican faith, postponed his registry office wedding. [The Age]
[T]hat the provinces … are to a greater extent dependent on public sector funding means, ipso facto, that they are first in line for the chop. [Independent]
When peace takes place, lands or territories do not become ipso facto restored, but are the subject of specific articles of agreement. [The New Monthly Magazine (1815)]
President Jacques Chirac’s contention that a lingua franca for the world – English or otherwise – ipso facto implies a common culture makes no sense. [New York Times]
The wealthy are, ipso facto, better, and shouldn’t be asked to play nice with others, or pay slightly more in taxes. [Paradise Post]
The publication of a book doesn’t ipso facto turn the author into an artist. [Daily Beast]
Mere hostile occupation, however, does not operate ipso facto to suspend the laws in force in the occupied territory. [A Treatise on the Military Law of the United States, George B. Davis (1913)]