Using a comma before which

Is there always a comma before which in a sentence such as - - . . . Scounted the possibilities at Countrywide Motor Sales which sells used sedans, station wagons and pickup trucks.

And . . . are restoring an old townhouse which will serve as a display shop for the . . .

I would just like to know the rule for which. Sometimes the grammer check on work says it calls for a semicolon.

Thank you.

[Raymott]

Originally Posted by Unregistered

Is there always a comma before which in a sentence such as - - . . . Scounted the possibilities at Countrywide Motor Sales[,] which sells used sedans, station wagons and pickup trucks.

And . . . are restoring an old townhouse which will serve as a display shop for the . . .

I would just like to know the rule for which. Sometimes the grammer check on work says it calls for a semicolon.

Thank you.

You use a comma before "which" in several places:
1. When the "which" clause refers to the whole preceding sentence:
"He punched me in the jaw and knocked me out, which I wasn't happy about.
2. Before a non-defining relative clause, as in your first example, and possibly the second. (I think the second example could go either way).

A defining relative "which" clause answers a "Which?" question.
"Which townhouse? The townhouse which will serve as a display shop"
A non-defining clause adds information, but does not define which townhouse you are referring to.
"We are building a townhouse, which will serve as a display shop."
"The orange tie which my wife bought me looks silly" (Answers "which tie?" from a sample of orange ties - the one which my wife bought me)
"The orange tie, which my wife bought me, looks silly." (Does not define which tie, but merely adds information.)

[RonBee]

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grammar checker at work