'Ipso facto' is a phrase sometimes used in English, derived from new Latin. It is composed of the ablative forms of 'ipse', meaning 'that', and 'factum', which is the perfect passive participle of the verb 'facere', 'to do', and means 'deed' or 'fact.' Its literal meaning is therefore 'by that fact.' But why should you care? And why would you use it? Read on…
In these egalitarian days, many people look askance at those who pepper their prose with Latin phrases. These are often thought to be a sign of pretension, useful merely for the flaunting of supposedly superior education, and contributing more to the obscuring of meaning than to the clarity of communication.
There are good reasons to be suspicious of the gratuitous use of foreign phraseology mined from a dead language. Modern English has been used for centuries as a vehicle of the highest-level discourse in almost every field of learning, as well as being the vernacular used by hundreds of millions of people spread across every continent of the Earth. It would be surprising if it were truly impossible to express any idea worth expressing using the native resources of the language.
However, a person who from time to time uses a Latin phrase is not ipso facto a pretentious poseur. The status quo of the language today should not blind us to the traces that its evolution has left upon it, and nor should the fact that some do indeed use Latin phrases in an attempt to appear erudite and/or to obscure the trivial nature of what they are saying lead us ab irato to condemn any usage of Latin under all circumstances. Ab abusu ad usum non valet consequentia! Many foreign words and phrases, not only of Latin origin, have been incorporated into English ab olim; some have been a part of normal (if not common) English usage for longer than many words now regarded as quintessentially English.
Latin phrases were originally introduced into English usage on an ad hoc basis by educated people who could assume that the people they were addressing would understand them, either because they could not think of the proper English term at the time, or because the Latin was more economical or precise, at a time when English did not yet have the great capacity and range I mentioned above. Although there was no general reason a priori for them to be preferred in the long term to the English equivalents where they existed, in some cases they were. In other cases the availability of a short Latin phrase understood by all obviated the need to establish an English locution at all. The Latin then became English.
Once a word or phrase has moved from one language to another it is free to acquire meanings and connotations that cannot be read out of a literal translation from one language to another. Thus the original motivation for introducing the term into the destination language becomes moot: originally it was used because it was clear to those who knew the source language. But now its proper understanding and use is a part of a command of the destination language.
An illustration of this last point can be found in the term ipso facto. As I explained above, its literal meaning in Latin is 'by/from that deed.' An approximate English equivalent in most contexts would be 'for that reason'. But there is more to 'ipso facto' than that. When someone uses 'ipso facto' they are ipso facto making a more precise point: that precisely that single reason that has just been cited is (or is not, in the case of negation) on its own and in and of itself a sufficient reason for what comes next. There is no more economical way of expressing this point available, and the correct use of 'ipso facto' is therefore ipso facto to be seen not as a sign of pretension or an offence against clarity, but simply as appropriate use of this wonderful English language. But don't worry: if you really want to be pretentious and obscure, you can always use 'eo ipso.'