Help with sentence: don't come in

Question

Which of the following is correct:

1) Don't come in, I'm busy.
2) Don't come in; I'm busy.
3) Don't come in. I'm busy.
4) Don't come in I'm busy.

And why?

Answer 1

Of the four choices, the only one that doesn't work is 4.

Don't come in, I'm busy.

is a comma splice, but acceptable informally.

Don't come in; I'm busy.

is perfectly fine, but a bit musty and over-educated for many uses.

Don't come in. I'm busy.

is probably the simplest, but may not express the connectedness of the two sentences sufficiently for your taste. (Note: It doesn't have to. Apposition is a form of connection.)

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Don't come in: I'm busy.

The colon indicates that "I'm busy" is a direct explanation of the command that comes before it.

But of the four I myself would go with No. 3.