Ampliative Argument
An ampliative argument is one whose conclusion goes beyond the information in the premises. Contrast with deductive arguments, where the conclusion is already contained in the premises.
Why go beyond deduction?
Deduction alone can’t grow knowledge; it just rearranges what you already know. Science, everyday belief, and prediction all rely on ampliative inference: from samples to populations, from observed to unobserved, from data to hypothesis.
Ampliative arguments are never deductively valid: the conclusion could be false even if all premises are true. But they can still be strong or weak, since good ampliative reasoning makes the conclusion more probable.
Forms
- Inductive generalization: from a sample to a population
- Statistical syllogism: from a population to an individual
- Inference to the Best Explanation: from observations to the hypothesis that best explains them
- Analogical argument: from similarities in known cases to similarities in unknown cases
- Causal inference: from correlation + design to causation
A deductive argument is judged by Validity + truth of premises (Soundness). An ampliative argument is judged by Cogency: strength of the inferential link plus true premises.
The deductive trap
Treating an ampliative argument as if it were deductive is a common mistake (see Affirming the Consequent: hypothesis testing looks like affirming the consequent but is legitimate when read as ampliative).