Argument from sign

You argue that something is the case by pointing to a telltale mark that usually goes with it. The argument works because the mark tends to appear when the claim is true, so seeing the one lets you infer the other, even though the mark did not bring the situation about. It can be attacked by showing that the mark is not distinctive — that many other things leave the same trace, so it points to nothing in particular.

Example

This movie must have been directed by Christopher Nolan because it has a non-linear plot

Standardised form

This movie (a) must have been directed by Christopher Nolan (X) because this movie (a) has a non-linear plot (Y).

Transformations applied: anaphora resolved — “it” replaced by “this movie”.

Classification

The subject is the same in both statements and the predicates differ, so the argument form is alpha (a is X because a is Y).

The conclusion “must have been directed by Christopher Nolan” is a statement of fact (F) and the premise “has a non-linear plot” is a statement of fact (F), so the argument substance is FF.

The keyword SIGN describes the relationship between predicates Y and X. The argument lever can thus be formulated as “Having a non-linear plot (Y) is a SIGN of having been directed by Christopher Nolan (X)”.

Not to be confused with

• Argument from cause — The premise names what produced the state in the conclusion, rather than a mark of it. CAUSE
• Argument from effect — The premise names what the state in the conclusion produced. EFFECT
• Argument from correlation — The two features are merely found together; neither is offered as an indicator of the other. CORRELATION
• Argument from criterion — Substance, not lever: the conclusion is a verdict rather than a matter of fact. VF

Source

Invented example.

Other examples

• “She (a) must admire Patricia (X) because she (a) is looking at her all the time (Y).” — invented example.
• “You (a) probably eat too much fruit (X) because you (a) are frequently bloated (Y).” — lilynicholsrdn.com, “5 signs you’re eating too much fruit”.
• “This mushroom (a) is poisonous (X) because this mushroom (a) has white gills (Y).” — invented example.
• “All human beings (a) by nature desire to know (X), because all human beings (a) have a liking for their senses (Y).” — Aristotle, Metaphysica 980a21–27, trans. T. Irwin and G. Fine (1995), Aristotle: Selections, Indianapolis: Hackett.