Evaluating Reasoning: Validity, Hidden Premises and Subtler Fallacies

Valid: if both premises are true, the conclusion must be true. Whether it is sound depends on whether the list really says that.

Valid: the conclusion follows from the premises. Sound: valid and the premises are actually true.

The team captain is the right person to speak for the team.

Begging the question: it says the lake carnival is the real one because the real one is on the lake; the conclusion is assumed in the premise.

Potholes on Queen Street have nothing to do with where the carnival is held; the sentence changes the subject.

The agreed test was cost (no more than the lake carnival). When that test was met, the writer changed the standard to quality (a worse carnival), without evidence.

Interpreting an argument in its strongest reasonable form before evaluating it.

Valid but not sound (the premise all birds can fly is false).

An enthymeme.

A loaded (complex) question: it presupposes the money is wasted.

Appeal to tradition.

Strong or weak.

Equal shifts from equal in rights (the law's meaning) to identical in traits. The argument only works by changing the meaning.

It is a tu quoque / ad hominem-type move: it attacks Councillor Ross's consistency rather than her reasons. Whether she skated last winter does not make the ice any safer or less safe now.

Charitable version: The lake carnival is a valued sixty-year tradition, and changing it would lose something the community cares about, so the town should keep it on the lake. Hidden premise: the value of the tradition outweighs the safety concern, a claim that needs support.

Sample: All Canadian cities get snow every winter. Victoria is a Canadian city. So Victoria gets snow every winter. Valid structure; the first premise is false (some winters in some cities have little or no snow).

Funding can be a reason for caution and further checking, but by itself it does not show the findings are false; that is a genetic fallacy (judging a claim by its origin). The fair response is to examine the methods and look for independent studies.

Sample: The carnival should stay on Mill Lake, with conditions. Ice-safety experts can test ice thickness weekly, as many communities do, and the town could set a minimum thickness for holding events, with Riverside Park as a backup if the ice falls short. The lake setting is part of what draws visitors, and the council's own budget shows the costs are equal, so keeping a tested lake carnival costs nothing extra while preserving a valued tradition. It gives reasons, addresses safety directly and uses evidence.

It can be sound but irrelevant to the real dispute, or rest on premises the audience does not accept or cannot check, or beg the question (circular arguments can be technically valid). Persuasion also depends on the audience's values and on whether the argument addresses their actual concerns.

Sample: it is overstated. Fallacy-spotting catches flaws, but evaluation also needs the charitable reconstruction, checks on whether premises are true and supported, attention to evidence quality, and awareness of what the argument leaves out. A fallacy-free argument can still rest on weak evidence, and a few weak moves do not make the whole position wrong (the fallacy fallacy).