In “What the Tortoise Said to Achilles,” Lewis Carroll explored modus ponens.
Modus ponens is the basic inference pattern: if P implies Q, and P is true, then Q follows. Carroll's 1895 dialogue turns that apparently simple rule into a philosophical puzzle. A tortoise accepts two premises about the equal sides of a triangle but refuses to accept the conclusion drawn from them.
Achilles responds by asking the tortoise to accept an additional conditional statement saying that, if the premises are true, the conclusion must be true. The tortoise then demands another conditional covering the expanded set of statements, and the process continues indefinitely. This creates an infinite regress.
The title itself alludes to Zeno's paradoxes, especially the race in which Achilles cannot overtake a tortoise. That reference explains why “Zeno's paradoxes” can look tempting as an answer, but the dialogue's actual logical focus is modus ponens. “Modus tollens” is a different valid inference rule: if P implies Q and Q is false, then P is false. Carroll's essay appeared in the philosophical journal Mind in 1895.