The Ex Ante, the usual expression in Economic vocabulary, corresponds to the more traditional expression in Law of A priori, and refers to the apprehension of a situation before it is constituted. For example, a law or a regulation is an ex ante act, which will regulate situations after the adoption of the text, of the decision or general disposition adopted by an authority. There is no retroactivity. Conversely, Ex Post, the usual expression in Economics and which corresponds in Law to the A posteriori, refers to a reaction of an organism to a situation or a behavior observed. Thus all individual decisions on sanctions, or all dispute or mediation settlements, come under ex post. For example, judicial acts fall under ex post.
Competition Law is usually recognized in that it develops in the ex post, since the market is established and the competition authority reacts to anti-competitive practices, which may be sanctioned, ie in ex post . Conversely, because it is a question of building competition or of maintaining non-natural balances on a permanent basis in sectors, Regulation Law uses tools that could be called "blank pages", essentially regulations, that is to say ex ante. This explains why the English term of "regulation" express at the same time the regulatory system as a whole and the texts adopted, the regulations (in French "réglementation"), because this ex ante tool is so important, is to intimate with regulatory spirit and perfectly expresses this ex ante distinguishing Regulation Law from Competition Law.
This opposition is fundamental because it not only sheds light on the distinction between competition and regulatory system, but also dictates the distribution and scope of powers. Indeed, to simply react ex post, it is enough to have a power to punish, to order reparations, to decide the different. Ex-ante intervention requires much greater powers since the regulatory authority dictates behavior in order to build markets and sectors. This magnitude of ex-ante powers explains that the title of regulator is so envied, and that even competition authorities sometimes present themselves as regulators of competition, as if constructing them beyond defending them, in particular by the adoption of provisional measures. Confusion is often made or even maintained by the oxymoron of "competitive regulatory system" made by these Competition Authorities, even if they are not limited to a specific sector.
This shows the fragility of the distinction between ex ante and ex post. Indeed, it may be open to criticism that competition authorities seek to appropriate ex-ante powers to exercise them on all markets, even though these markets do not justify the exercise of regulatory mechanism, but it is true that it exists a continuum between ex ante and ex post. This continuum is exercised in both directions. In the sense of the ex-ante to the ex-post, it is the Regulator himself who, after having taken the ex ante standards, ensures its effectiveness through continuous monitoring and sanctioning failures.
Moreover, in the sense of the ex-post to the ex-ante, because, as gaming theory shows, especially in the banking and financial markets, agents are anticipatory, a decision to sanction or to settle different is interpreted as a signal, for example of severity or warning, of tendency, a kind of act of doctrine of authority, that the operators have integrated into their future behaviors. Thus, the ex post act becomes the cognitive ex ante.