Ex-Ante & Ex-Post

From Justice Definitions Project

What is ex-ante & ex-post?

The ex-ante and ex-post terminology is derived from law and economics and is generally used in finance for predicting returns on a security, price fluctuations and determining income. This word is mostly used in business, where the outcomes of a certain action or set of actions are predicted ahead of time or after an event.

"Ex-ante" means "before the event" in English, while "ex-post" means "after the event." To put it simply, ex-ante means "looking ahead" and means predicting what will happen in the future. On the other hand, ex-post looks at results that have already happened, or after the fact.

After the event that was predicted (ex-ante) takes place, experts can compare it to what actually happened (ex-post) to see how accurate the prediction was. In general, economists have seen ex ante and ex post measures as different ways to fix externalities. For example, an ex-ante policy is to test drugs before they are licenced, while an ex-post policy is to hold drug companies strictly responsible for their products. The difference between the two results can help one figure out how to speed up the prediction process so that it is almost perfect. Also, it helps the experts see how well they did compared to what they had originally planned to happen.

Official definition of ex-ante

The ex ante point of view looks ahead. In simple terms, it's predicting what will happen before it does, and the real result is unknown. After forecasting what will happen, the ex-ante value can be compared to how well it actually works when it does happen.

The common phrase in economics is "Ex Ante," which is the same as the more traditional phrase "a priori" in law. Simply put, ex ante examination in the law looks into what the situation was like before an event. This type of examination is future and subjective. As an example, a law or rule is an ex ante act because it controls what can happen after the text, decision, or general disposition of an authority is made public. There is no going back in time.

Questions such as "What will happen in the future because of this rule?" arise from the ex ante point of view. Mostly, policy and welfare are linked to the ex ante viewpoint. The ex ante view in legal theory is related to consequentialist moral theories in a roundabout way. It can be linked to either legal instrumentalism or legal realism in general law.

Official definition of ex-post

The ex post view looks at things from the past. Questions such as "Whose rights were broken?” need to be answered. Fairness and rights are linked to the ex post viewpoint. There is a link between the ex post viewpoint in legal theory and deontological approaches to moral theory. In general jurisprudence, it is associated with post perspective with legal formalism.

Ex Post, in economics, is similar to the phrase “a posteriori” in law, means how an individual responds to a situation or behaviour that was seen. In this way, all decisions made by individuals about sanctions or all agreements reached through mediation or a disagreement fall under ex post. Ex post review in law looks at everything that happened after the fact; it is objective and looks at the past.

When it comes to tort law, for instance, corrective justice theories of tort are linked to the ex post viewpoint i.e., A should only have to pay B if A did something wrong.

Research that engages with ex-ante & ex-post

The fundamental inquiry concerning legal transitions, which has surfaced in the fields of philosophy and economics, concerns if and when it is permissible for the government to offset ex post consequences of its ex ante decisions.[1]

Ex ante regulations, such as safety standards, which govern an activity prior to the occurrence of an accident, have been perceived by economists as viable alternatives to ex post policies, which use tort liability in order to rectify externalities. Ex ante regulation can help rectify inefficiencies that occur with the exclusive application of negligence liability in situations where uncertainty exists.[2]

Furthermore, it has enormous ramifications for intellectual property rights.[3] The conventional rationale for intellectual property is ex ante: its purpose is to exert influence over actions that take place prior to the right's establishment. Creative incentives are encouraged by the hope of obtaining intellectual property rights. Further consideration must be given to ex post justifications that intellectual property rights provide the proprietor with effective incentives to improve or develop an existing creation and that they regulate the use of information.[4]

In data privacy-related legislations, ex-ante measures pertain to data transmission regulations, whereas ex-post measures concern the enforcement of privacy rights.[5]

Competition law usually stems after the market is set up and anti-competitive actions have been taken, which means that the law is ex post. At present, India's legal framework exclusively employs an ex-post regime, which entails resolution of issues subsequent to the occurrence of harm.

Alternatively, regulation law or regulations, are made before a competition concern arises. Ex-ante measures are required by competition law to prevent enterprises in a dominant position from engaging in abusive anticompetitive practises. This is used to build competition or maintain regular market forces. Such an ex ante tool is important for promoting the regulatory spirit and helps differentiate regulation law from competition law.[6]


  1. Barbara H. Fried, Ex Ante/Ex Post, 13 Journal of Contemporary Legal Issues 123 (2003)
  2. Kolstad, Charles D., Thomas S. Ulen, and Gary V. Johnson, “Ex Post Liability for Harm vs. Ex Ante Safety Regulation: Substitutes or Complements?” The American Economic Review 80, no. 4 (1990): 888–901, available at http://www.jstor.org/stable/2006714
  3. Lemley, Mark A, (2004) "Ex Ante versus Ex Post Justifications for Intellectual Property," University of Chicago Law Review: Vol. 71: Iss. 1, Article 9
  4. Ibid
  5. Granmar, Claes Gustav, "Ex-Ante Measures Regarding Data Transfers and Ex-Post Enforcement of Rights", available at https://europeanlawblog.eu/2022/07/08/ex-ante-measures-regarding-data-transfers-and-ex-post-enforcement-of-rights/
  6. Ex Ante / Ex Post, Marie-Anne Frison-Roche, available at: https://mafr.fr/en/article/ex-ante-ex-post2/#:~:text=The%20Ex%20Ante%2C%20the%20usual,situation%20before%20it%20is%20constituted
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