Group of words in a sentence that function as a single part of speech. Does not contain a subject or a verb. Cannot stand alone.
Starts with preposition - ends with noun/pronoun. ONLY use commas with preps at the beginning of a sentence (if you want to - usually if they are large or require a pause - author choice)
Form of ING verb with modifiers that acts as an adjective. When it starts or interrupts the sentence, you use a comma or commas.
To + a verb with modifiers. When it starts or interrupts, use comma/commas.
Noun/pronoun with modifiers. It RENAMES the noun before it. Almost always surrounded by commas. Appostives are NEVER introductory!
Can be word(s), phrase, or dependent clause. Starts the sentence. If you take it out, you still have a sentence. Must be followed by a comma. Helps sentence variety.
Interrupts a sentence - Not essential. Must be surrounded by commas