Homonyms.

Homonyms. A relatively small number of homonyms—just eight groups—cause writers the most frequent trouble.

accept (to take or receive) to (in the direction of)
except (to leave out) too (in addition; excessive)
affect (an emotion; to have an influence) two (number between one and three)
effect (a result; to cause to happen)

weather (climatic conditions)

whether (if)

its (possessive of it)

it’s (contraction of it is or it has)

who’s (contraction of who is or who has)
their (possessive of they) whose (possessive of who)
there (in that place) your (possessive of you)
they’re (contraction of they are) you’re (contraction of you are)

If you tend to confuse particular homonyms, try creating a special memory device to help you remember the differences between the words. For example, “We all complain about the weather” will remind you that weather (the climate) starts with we.

In addition, pay close attention to homonyms that may be spelled as one word or two, depending on the meaning.

Of course, they did not wear everyday clothes every day.

Before the six lawyers were all ready to negotiate, it was already May.

The director may be on time. But maybe she’ll be late.