You call 911 and whisper to the operator, “There’s a prowler in the bushes just outside my window.” What if the operator says to you, “Bushes around a house can cut down on heating expenses”?

It isn’t a question of whether that’s true or not; it’s a question of how it matters right at this moment. The point of your call is not about the bushes, even though you mentioned them. The general topic may include the bushes, but the point of your call is the prowler. The bushes and heating expenses are not relevant at this time.

What if the operator asks you if you’ve heard of any prowlers in the neighborhood in the past? Suppose you say no, and the operator says, “Well, then, I wouldn’t worry about it. If there haven’t been any prowlers in the past, there probably aren’t any tonight either.”

What would you say? You would probably say you want to talk to someone else. You could also whisper to the operator that he is making an invalid inference. What he is saying doesn’t follow from what you told him. Just because there haven’t been prowlers in the past doesn’t mean the person in the bushes is not a prowler.

Just like prowlers who can creep around and get into places they don’t belong, irrelevant information and invalid inferences can creep into your expository writing. In this lesson, you will learn how to make the information in your expository essays relevant and your inferences valid.