Ex post facto - a posteriori

[Thomas Schlemmermeyer]

Dear All,

Recently, I read in a quite interesting paper, written in English, the Latin
expression "ex post facto".

My impression is that the author used this expression in cases where I would
have used "a posteriori".

Further, I got the impression, that the author used "ex post facto" , as
opposed to "a posteriori", in order to emphasize the cirumstance that the
explanation was given after the fact already had happened rather than the
circumstance that the author gave an explanation after having carefully studied
the subject under question (instead of giving a priori guesses).

I do not know whether I was able to express correctly my point in English.

But if anyone has more hints about the differential use of "ex post facto"
and "a posteriori", I will be grateful.

  Cheers,  Thomas