Definition

1. Adverb:
   • With greater reason; for a still stronger, more certain reason: Used to indicate that a conclusion follows even more logically or convincingly from a premise than a previous conclusion does. It is a logical term meaning "from the stronger [argument]."

Usage

• The term a fortiori is used in formal, logical, or legal arguments to strengthen a point. It introduces a statement that is considered even more certain or true than one just accepted.
• It is typically placed at the beginning of a clause or sentence.

Examples

• Adverb:
  • If a law is unconstitutional for a state government, then, a fortiori, it is unconstitutional for a federal agency to enforce it.
  • He cannot be trusted with simple tasks; a fortiori, he should not be given a position of major responsibility.
  • The reference example: "If you are wrong then, a fortiori, so am I."

Advanced Usage

• In Legal Reasoning: The principle is frequently used in judicial opinions to argue that if a rule applies in a less obvious case, it must apply with even greater force in a more obvious one.
  • If entering a home without a warrant is prohibited, then a fortiori, secretly installing a camera inside it is also prohibited.
• In Philosophical or Logical Discourse: Used to draw a comparative, strengthened inference.
  • If it is wrong to cause suffering to humans, then it is, a fortiori, wrong to cause greater suffering.

Variants and Related Words

• A priori (Adverb/Adjective): Refers to reasoning or knowledge that is independent of experience (deduced from theory rather than observation). While both are Latin logical terms, they have distinct meanings.
• Logical inference: The process of reaching a conclusion based on evidence and reasoning.

Synonyms

• All the more so
• With even stronger reason
• By stronger argument

Notes

• A fortiori is a Latin phrase adopted into English. It is used almost exclusively in formal, academic, or legal writing and speech.
• There are no direct phrasal verbs or idioms derived from this specific term, as it is itself a fixed logical idiom.

Adverb

1. with greater reason; for a still stronger, more certain reason
   • if you are wrong then, a fortiori, so am I