You argue that a claim about what happened should be accepted because someone who was there says so. The argument works because the source is credited not with expertise but with a place at the scene: they were in a position to see or hear it, so their report stands in for the event itself. It can be attacked by questioning whether the witness really had that position, saw clearly, and remembers accurately.
Example
The blue van went through the red light; the woman waiting at the bus stop on the corner saw the whole thing
Standardised form
“The blue van went through the red light” (q) is acceptable (A) because “the blue van went through the red light” (q) is said by the woman who was waiting at the bus stop on the corner (Z).
Transformations applied: the semicolon replaced by “because”; “saw the whole thing” transposed into the premise as the attribution of the claim to its source; the claim’s acceptability made explicit as the conclusion-predicate.
Classification
The conclusion is referred to as a whole in the premise, so the argument form is delta (q is A because q is Z).
The premise attributes the conclusion to a third party, so the argument substance is III.
The keyword TESTIMONIALLY AUTHORITATIVE describes the relationship between predicates Z and A. The argument lever can thus be formulated as “Being said by the woman who was waiting at the bus stop on the corner (Z) is TESTIMONIALLY AUTHORITATIVE for being acceptable (A)”.
Not to be confused with
- Argument from expert opinion — The source is credited with knowing the subject, not with having been present.
EPISTEMICALLY AUTHORITATIVE - Argument from moral authority — The source is credited with standing to say what is right.
MORALLY AUTHORITATIVE - Argumentum ad populum — Authority is a matter of numbers, not of who saw what.
POPULARLY AUTHORITATIVE - Ethotic argument — The arguer vouches for their own claim.
I
Source
Invented example.
Notes
See the note on the argument from expert opinion.
PERIODIC TABLE OF ARGUMENTS 