Does a comma always come before as you know?

No, a comma doesn't always come before "as you know." It depends on the structure and purpose of the sentence.

Here's a breakdown:

When to use a comma:

* Parenthetical phrase: If "as you know" is a parenthetical phrase, meaning it could be removed without changing the sentence's meaning, you use a comma on both sides.

* Example: "The meeting is tomorrow at 2 pm, as you know."

* Introductory phrase: If "as you know" is an introductory phrase, you use a comma after it.

* Example: "As you know, the project is due next week."

When to NOT use a comma:

* Integral part of the sentence: If "as you know" is an essential part of the sentence's meaning, you don't use a comma.

* Example: "I know you're busy, but as you know, this is important."

It's always best to analyze the sentence structure to determine if the phrase is parenthetical, introductory, or essential to the meaning.