Commas That Change the Meaning of Your Sentence

Compare 'Let's eat, Grandma' with 'Let's eat Grandma'. The comma of direct address is doing serious work.

Defining versus non-defining clauses: 'My brother who lives in Delhi is a doctor' implies several brothers. 'My brother, who lives in Delhi, is a doctor' implies one.

Use a comma before a coordinating conjunction that joins two full clauses: 'She studied hard, and she passed.' No comma when the subject is not repeated: 'She studied hard and passed.'

Introductory elements take a comma: 'After the exam, we celebrated.'

Do not separate a subject from its verb with a single comma, however long the subject is.