A commonly cited usage error is that of mixing up the verbs imply and infer.
Here are some examples from the Web:
Incorrect: My girlfriend inferred it was over without actually saying it.
Correct : My girlfriend implied it was over without actually saying it.
Incorrect: In your letter, you infer that your partner is over 18.
Correct : In your letter, you imply that your partner is over 18.
Incorrect: I didn’t mean to infer by my remarks that the business doesn’t have the correct zoning.
Correct : I didn’t mean to imply by my remarks that the business doesn’t have the correct zoning.
Plenty of literary examples can be found in which educated writers of the past have used infer in the sense of imply, but modern standard usage finds it useful to draw a distinction between these two words, reserving imply to mean “to hint or suggest” and infer to mean “to extract meaning from some kind of evidence.” For example:
The suspect’s silence implied that he would not cooperate with the police interrogator.
The police interrogator inferred from the suspect’s silence that further questions would be useless.
Here is how some stylebooks explain the usage:
Chicago Manual of Style
The writer or speaker implies (hints, suggests); the reader or listener infers (deduces). Writers and speakers often use infer as if it were synonymous with imply, but careful writers always distinguish between the two words.
Associated Press Stylebook
Writers or speakers imply in the words they use.
A listener or reader infers something from the words.
Guardian/Observer Style Guide
“to infer” is to deduce something from evidence; “to imply” is to hint at something (and wait for someone to infer it)
Penguin Writer’s Manual
These two words [imply and infer] are sometimes confused, though they in fact are opposite in meaning. To imply something is to suggest it by what you say without stating it explicitly. To infer something is to deduce it from what someone says, even though they have not explicitly said as much. That said, the use of infer to mean the same as imply has become increasingly common.
A Dictionary of Modern English Usage
This misuse of infer for imply is sadly common–so common that some dictionaries give imply as one of the definitions of infer without comment. But each word has its own job to do, one at the giving end and the other at the receiving and should be left to do it without interference.