If valid, which principle best justifies the scientist's reasoning?

• A. The conclusion follows logically from the premises.
• B. The conclusion is true if it is popular.
• C. The conclusion is supported only by anecdotal evidence.
• D. The conclusion is valid if it has no counterexamples.

Answer: (A)

Reasoning is justified when the conclusion follows logically from the premises. If the premises are true and the argument form is valid, the conclusion must be true; the chain of reasoning shows the conclusion is a necessary consequence of what was stated or evidenced. That direct link is what gives scientific arguments their strength: the conclusion is a logical outcome of the premises.

The other ideas don’t establish that guaranteed connection. Popularity isn’t a measure of truth, so it can’t validate the reasoning. Anecdotal evidence is weak support and doesn’t establish a reliable logical bridge from premises to conclusion. And having no counterexamples is not the same as validity, because there could be unseen cases or the premises might not actually entail the conclusion.