It’s easy to fall back on shorthand, to use words that pack rhetorical punch and don’t require explanation. Words like these  (“conservative,” “millennial,” “freedom”) are general enough but also can be understood in a specific way by a specific audience; indeed, one way we forge tribes is that the in-group knows what you mean without your having to spell it out. But the ambiguity of these terms can also lead to miscommunication. More often, it leads to muddled thinking.

Terry Eagleton asks us to add “evil” to this list. So I set a Google News alert for the word, and almost immediately got results as varied as: voting for Roy Moore, tax cuts, gay rights, a school shooter, loneliness, Sarah Huckabee Sanders, and the New York Yankees. We use the word enough. So what are we talking about?

In On Evil, Eagleton tries to give us an answer. He’s troubled that we refer to terrorists as evil; not because their actions aren’t heinous, but because we might not even be sure what we mean by it. Eagleton observes, “The word ‘evil’ is generally a way of bringing arguments to an end, like a fist in a solar plexus,” because it is meant to end the asking of explanatory questions. In the popular way we discuss evil, Eagleton writes, “either human actions are explicable, in which case they cannot be evil; or they are evil, in which case there is nothing more to be said about them.” The point of the book is to demonstrate that neither of these things is true.

It is easy to invoke the e-word, Eagleton explains, because we assume that evil is “uncaused.” In this (incorrect) view, someone who is evil has no excuse; their actions result from their freely chosen character. They’re “just evil.” Suggesting that there might be an external reason, that someone can do something evil “rationally,” might invite accusations of trying to justify an evil action. For politicians especially, suggesting there are rational motives for terrorism is not a smart PR move.

So if this is the wrong way to conceive of evil, what’s the right way? Eagleton lists a few of evil’s characteristics. It is uncanny—almost real, but a shadow of itself. It is superficial, presenting itself as one thing but turning out to be another. It is an assault on meaning; it wishes to undo reality and expose the universe as a sham. It is monotony, forever; Eagleton warns sinners, “Hell is being talked at for all eternity by a man in an anorak who has mastered every detail of the sewage system of South Dakota.”

Ultimately, evil is a disposition, one that “takes up an attitude toward being as such…Fundamentally, it wants to annihilate the lot of it.” It is a refusal to acknowledge the reality of things, one’s place in the world, and the inherent goodness of being. Satan revolted against God’s order, and sought to destroy. But Eagleton explains that Satan is in a “perpetual sulk”; even in willing the destruction of reality, he is defeated because his own act of destruction acknowledges that something exists in the first place.

Eagleton’s book is full of such insightful and entertaining observations, and he often uses literary or historical evidence to great effect. But the book is also full of digressions, half-answered questions, and unexplained terms as well. At some point he makes a distinction between “evil” and “wickedness,” with wickedness being the more common of the two, but he never gets to explaining why. The answers that I was really hoping for—Are we evil? Is evil an everyday occurrence or a heinous rarity?—never really materialize. On the one hand, he writes, evil is subtle and ever-present; on the other, wickedness is primarily institutional, so evil is “not something we should lose too much sleep over.”

But maybe On Evil is necessarily incomplete, an exploration more than a treatise. One of Eagleton’s best observations is that “flaws, loose ends, and rough approximates are what evil cannot endure…Goodness, by contrast, is in love with the dappled, unfinished nature of things.” If that’s true, I’ll try to be content with more questions than answers for now.