Can You Start a Sentence with a Preposition? | Grammar Girl
www.quickanddirtytips.com › education › grammarJul 12, 2013 · Commas After Prepositional Phrases at the Beginning of a Sentence. When you start a sentence with a prepositional phrase, it's usually a good idea to put a comma after it (as in the examples above). In general, the longer the prepositional phrase, the more you need the comma. For example, the Purdue Online Writing Lab says a comma is required after introductory prepositional phrases that are longer than four words.