So while he sometimes does massage his own statements — as he tried to do last month after his remarks on punishing women for getting abortions — Mr. Trump is most effective when he simply says the opposite of what he said before. In part, that’s because Mr. Trump’s contradictions are loud and confident. (“I love Hispanics!” he tweeted on Thursday, Cinco de Mayo, along with a picture of him with a taco bowl.) But it is also because when a person says something as well as its opposite, his listeners can infer that he really believes whichever statement they wish him to believe.

That contradictions are particularly useful to Mr. Trump also tells us something about what some people find appealing about him. Indeed, it reveals an even deeper contradiction. Mr. Trump’s explicit lack of authenticity is what makes him so authentic. He is like a walking oxymoron (which is perhaps not surprising, given that reality TV is the medium in which he has most flourished). To some, that he is contradicting himself so freely shows that he really doesn’t care what “they” (read: the news media, liberals, women, minorities) think. The signal this sends is one of strength: Only the strong can afford not to care.

There is also a deeper philosophical issue here. The most disturbing power of contradiction is that its repeated use can dull our sensitivity to the value of truth itself. That’s particularly so given that most Americans live in a digital world that both makes it easier and harder to figure out what is true. Googling is like being in a room with a million shouting voices. It is only natural that we’ll hear those voices that are most similar to our own, shouting what we already believe, and as a result Google can find you confirmation for almost anything, no matter how absurd.

Of course we are aware that those with different views can do the same. And that very fact, if we aren’t careful, can lead us into thinking that objectivity is a “dead value.” We get so used to contradictory information, rival sources, that we find ourselves no longer valuing truth.

In George Orwell’s “1984,” the protagonist is tortured until he agrees that two plus two equals five. The point, his torturer makes clear, is to make him see that there is no objective truth other than what the party says is true. That’s the deep power of contradiction. Repeated enough, political contradictions can lull us into giving up on critical thought altogether. And once that happens, we risk giving up on truth. At which point contradictions — and everything other than power — will no longer matter.