Is there a difference between comparing A to B and comparing A with B?

The answer is yes, and it is a difference worth maintaining; but these days, compare to and compare with are in danger of becoming interchangeable. This looks like yet another fight that the grammar patrol is about to lose.

When we compare something to something else, we are placing two things—sometimes very different things—in the same category and commenting on connections we perceive. We are expressing an opinion or making an observation. Others might not have noticed these similarities; still others might disagree with them. Some examples: I’d compare the view from your living room to a painting by Bierstadt. Ruben compared Giorgio’s spaghetti to dog food. Note that these are subjective statements—they are not verifiable.

When we compare something with something else, we are not expressing opinions or making personal statements. We are placing two things side by side and noting empirical similarities and differences. Our purpose is to be fair and impartial. The accuracy or inaccuracy of our findings can be verified. For instance, if we flout the old cliché and compare apples with oranges, we find that neither fruit contains fat, cholesterol, or sodium; that oranges contain more than twice as much potassium as apples; that a cup of oranges contains twenty more calories than a cup of apples.

The act of comparing to—claiming that two distinct entities share a noteworthy similarity—is something children do all the time. When a child says, “Mommy, that owl looks like Uncle Al!” she is comparing her uncle’s face to a bird’s. That is not exactly in-depth analysis. Comparing with tends to be a more mature, responsible, and demanding act than comparing to. Comparing with requires objectivity—and often necessitates research.

In the writer’s guide Simple and Direct, Jacques Barzun issues this caveat: “Any writer can compare himself with Shakespeare and discover how far he falls short; if he compares himself to Shakespeare (i.e., puts himself on the same level), then he had better think again.”