The UVic Writer's Guide

Matt has been improving at school. Since he stopped skipping class.

It was the time of year when the neighbours would suddenly become uncharacteristically generous, pressing quantities of enormous zucchini on us. It being the most prolific of vegetables.

The sentences must be reconnected:

Matt has been improving at school since he stopped skipping class.

It was the time of year when the neighbours would suddenly become uncharacteristically generous, pressing quantities of enormous zuccini on us, it being the most prolific of vegetables.

Every sentence must have a main clause, and thus a complete verb.

Particularly in works of fiction, a sentence fragment can be a rhetorically effective device, but in formal writing it is more likely to be simply inept.

A tip: if you are unsure of the distinction between a complete verb and an incomplete one, or a main clause and a participle phrase, there is a simple test you can apply to find out if you have a sentence fragment, or a comma splice:

• Each complete sentence will make a complete statement, and each complete statement must be either true or false.
• Thus if you ask of the fragment above--"Since he stopped skipping class": true or false--there can be no answer (what happened since he stopped?), and thus it is not a complete sentence.
• Similarly, both parts of the comma splice can be tested ("They believed in Oedipus" and "He is their king"--both can be answered, in this case as "true"), so there are two complete statements.