Comma before "i.e." is required when:
* "i.e." is used to clarify or explain a previous phrase or word. It acts like a parenthetical expression.
* Example: "We need to buy groceries, i.e., milk, eggs, and bread."
Comma before "i.e." is optional when:
* "i.e." is used to introduce an example that follows a list.
* Example: "There are many options, i.e., fruit, vegetables, or cheese." In this case, the comma is optional, but often preferred for clarity.
Comma before "i.e." is not required when:
* "i.e." is integrated into the sentence flow and not a separate phrase.
* Example: "The i.e. stands for 'id est', which means 'that is' in Latin."
Key takeaway:
The rule of thumb is to use a comma before "i.e." if it acts like a parenthetical expression or introduces a clarifying example.
In summary, it's best to consider the context and the overall flow of the sentence when deciding whether or not to use a comma before "i.e."