They are related insofar that they both have something to do with figuring out a piece of information that isn’t completely expressed by the other party, but that doesn’t mean that the two words can be used interchangeably.
Imply: to strongly suggest the truth or existence of something not explicitly stated
If person A is saying something to person B, then person A may be implying something as part of that speech. Let’s say, for instance, that I tell you I “wouldn’t go” to a certain restaurant. By doing that, I imply that either the food or the service isn’t very good at that restaurant. I am saying this in an indirect manner.
If I told you that James flunked out of high school, then I may be implying that he isn’t very intelligent. Similarly, you may recognize that correlation does not imply causation. The observation of a correlation does not necessarily give you reason to believe that a causal relationship also exists.
Infer: to derive, speculate, or conclude based on reasoning
This is almost the flip side. Whereas the speaker (or source material) is the one doing the implying, it is the listener (or reader, etc.) who is doing the inferring. An inference is supposed to be based on logic, both deductive and inductive.
For instance, all cars have four wheels. A Ferrari is a car. Therefore, I can infer that a Ferrari has four wheels. This is a logical conclusion based on the two facts that we already know. If a politician at a debate is singing praises for a new policy, then the audience can infer that the politician would vote in favor of that new policy.
Thanks to Lesley for suggesting today’s topic. Do you have a grammar question that you’d like to see addressed in a future post? Let me know through the comments below.