Fortiori analysis – definition and meaning

A fortiori analysis is a way of treating uncertainty that strengthens the case for a preferred choice of action by stacking the cards against alternative options. If after extensively looking at the pros (and cons) of the alternatives to your preferred choice, that one remains preferable – the case in its favor is strengthened.

The first half of this article looks at the meaning of ‘a fortiori analysis’, while the second half focuses on the meaning of ‘a fortiori’ (without the word ‘analysis’).

A fortiori analysis, in decision theory, is an analysis that is made to deliberately favor alternative solutions when compared to a solution that was judged to be the preferable one.

The pros of the alternatives are intentionally given additional weight, to make them look better. If the original solution still seems to be the best option, it will be easier to choose, because that choice has been further strengthened after comparing it to alternatives.


A Fortiori AnalysisWith ‘a fortiori analysis’, you look at alternatives to your preferred option, and exaggerate their pros. If your preferred option remains the best, you will be more certain about your decision.


According to Business.Dictionary.com, a fortiori analysis means:

“In decision theory, an analysis made to intentionally favor alternative solutions when compared to the solution adjudged as best. The alternatives are deliberately weighted to make them look better.”

“If the adjudged-best solution still remains the best, its position as the likely choice is further strengthened.”



Argumentum a fortiori

Argumentum a fortiori is a way of arguing that one thing is certain because another thing has been established – if one thing is implicit, then you can be certain of several other things.

For example, if a man is dead (the implicit thing), then I can with equal or greater certainty argue a fortiori that the man is not breathing. ‘Being dead’ triumphs over any other argument that might be put forward to show that he is dead.


Argumentum a fortioriLegal-Dictonary.TheFreeDictionary.com says the following regarding the term ‘a fortiori’: “[Latin, With stronger reason.] This phrase is used in logic to denote an argument to the effect that because one ascertained fact exists, therefore another which is included in it or analogous to it and is less improbable, unusual, or surprising must also exist.”


If the law states that anybody who exceeds the speed limit by 10 mph is liable for a $100 fine, one can infer a fortiori that anybody who exceeds the speed limit by 20 mph is also liable for a fine of at least $100.

A fortiori is Latin for ‘more conclusively’ or ‘even more so’.



Video – A Fortiori

This Speak Legal video explains what a fortiori means, and clearly shows how the term is pronounced. The speaker gives an example of a person who is too young to be an administrator. This person has a younger brother, who most definitely – a fortiori – is too young for the job.