Explanation:

Let's use an example to illustrate these concepts. "If it is raining, then it is cloudy." Let's discuss all aspects of this claim to make sure there is no confusion. First, the claim is true. Rain comes from clouds. Now sometimes it is sunny and raining. That's an unusual experience, but it happens. However, there must be a cloud somewhere, because that's the only place rain comes from. So whenever the first condition is present (it is raining), the second condition is certain to be present (it is cloudy).

The consequent is also called the "necessary condition."
Remember that the consequent follows "then." That means there is always a relationship between the first part of the sentence (If____,) and the second part (then___). And the relationship works this way. Whenever the first condition is present, then the second condition MUST be present. In other words, it is NECESSARY that the second condition be present. For instance, every time that it rains, it is NECESSARY that it be cloudy. It has to be cloudy in order for there to be rain (at least a little bit cloudy).

The antecedent is also called the "sufficient condition."
This means that whenever this condition is present, for instance, "it is raining," that this is SUFFICIENT to guarantee that the consequent is present. In other words, that is all it takes to ensure the consequent. The presence of rain is all it takes to guarantee that it is cloudy. Or, rain is sufficient for clouds. So, whenever rain is present, clouds are present - guaranteed.

Does it work both ways? NO. Here's why.

First, think about it for a moment. Does it always rain when there are clouds? Of course not. Sometimes it's cloudy and there is no precipitation. Other times it might snow, sleet, or hail. The presence of clouds in no way guarantees that it is raining. In other words, saying "If it rains, then it is cloudy," is not at all the same as saying "If it is cloudy, then it is raining." Conditional claims only work in one direction.

Every conditional claim has one sufficient condition and one necessary condition. The antecedent = the sufficient condition. The consequent = the necessary condition.

Beyond the grammatical structure of the conditional claim, it is important to evaluate the actual relationship between the clauses. Is the stated relationship actually the case?

For instance, "If Bill Clinton is president, then the moon is full." Bill Clinton is president and sometimes the moon is full. But is Bill Clinton's being president enough to make the moon full? Of course not. So even though we can randomly plug independent clauses into conditional claims, it does not mean the conditions are actually sufficient or necessary. Again, one must evaluate the logical structure as well as the truth of the content.

Practice Exercise