Here's why:
* "Also" is an adverb: It modifies the verb or the entire clause, but it doesn't introduce a separate clause.
* Comma use: Commas are used to separate clauses, items in a list, or to set off introductory phrases. "Also" doesn't fit any of these categories.
Example:
* Incorrect: Also, the cat is sleeping on the couch.
* Correct: Also, the cat is sleeping on the couch.
Exception:
If "also" is followed by a parenthetical phrase or a phrase that could be mistakenly read as a separate clause, you might use a comma for clarity.
Example:
* Correct: Also, the cat, which is very fluffy, is sleeping on the couch.
Let me know if you have any other grammar questions!