Fortiori analysis – definition and meaning

A fortiori analysis is a way of treating uncertainty that strengthens the case for a preferred choice of action. With the ‘a fortiori analysis’ method, you stack the cards against alternative options. If, after extensively looking at the pros and cons of the alternatives, that one remains preferable – you have strengthened the case in its favor.

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

A fortiori analysis – decision theory

We use a fortiori analysis in decision theory. In the analysis, we deliberately favor alternative solutions when comparing them to an option that we judged to be the preferable one.

We intentionally give additional weight to the pros of the alternatives. We deliberately make the pros of the alternatives look better than they are.

If the original solution still seems to be the best option, it will be easier to choose. Choosing is easier because we have further strengthened that choice after comparing it to alternatives.

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

According to, 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 we have established another thing. If one thing is implicit, then you can be certain of several other things.

For example, if a man is dead then I can with equal or greater certainty argue a fortiori that the man is not breathing. The man’s death is implicit. ‘Being dead’ triumphs over any other argument that we might be put forward to show that he no longer lives.

Imagine a country where there is a speed limit on the roads. Anybody who exceeds that limit by ten miles per hour faces having to pay a $100 fine. We can infer a fortiori that drivers who exceed the limit by 20 mph also face having to pay a $100 fine.

Imagine you see a newborn baby in a maternity hospital. You can then with equal certainty argue that the baby does not have a driving license. It is clear that the baby is too young. ‘Being a newborn baby’ triumphs over all the other arguments to show that he may have a driving license.

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