Is at a preposition and does it require comma?

"At" is a preposition, but whether it requires a comma depends on the context. Here's a breakdown:

When "at" does NOT require a comma:

* When it's part of a prepositional phrase that modifies a noun or pronoun:

* Example: "The dog was at the park."

* When it's used to indicate time or location:

* Example: "I'll be there at 3 pm."

When "at" MAY require a comma:

* When it introduces a parenthetical element:

* Example: "The meeting, at least according to the schedule, is at 2 pm." (The phrase "at least according to the schedule" is parenthetical)

* When it introduces a dependent clause that follows an independent clause:

* Example: "I went to the store, at which point I realized I forgot my wallet." (The clause "at which point I realized I forgot my wallet" is dependent on the first clause)

Remember: The best way to know if a comma is needed is to read the sentence aloud and listen for natural pauses. If a comma sounds right, then it probably is.