I'm reading Zeno's paradox, and it says that Achilles could never pass the tortoise, and then it says: "This defies common sense". But what's the meaning of "This defies common sense." ?
The dictionary definition for common sense is "good sense and sound judgement in practical matters." I would like to refer to this as "everyday reasoning".
Everyday reasoning tells us that since Achilles can run a lot faster than a tortoise can move, he will at some point overtake it. Zeno's paradox tries to persuade us that this won't happen since the tortoise will always remain ahead of Achilles, no matter how fast Achilles runs. However, it is based on a logical fallacy that, in the end, reduces to the fact that the tortoise will remain ahead of Achilles until the moment that Achilles overtakes it.
Zeno's paradox seems to contradict everyday reasoning (common sense) but it doesn't really since it is based on a fallacy. In this sense, it can be said to "defy common sense". However, correctly applied logic will show that Zeno's paradox is not really a paradox at all. It is just a misleading and erroneous argument.