Dictionary of English - comma

Commas are also used to mark off sentence connectors such as however, nevertheless, moreover: Nevertheless, I can say, without any doubt, that he deserved his success. There are other occasions where a comma is needed to indicate a pause or a slight change of direction in the sentence. For example, I certainly won't see him again, although I can't help liking him. Commas are often incorrectly used where a stronger stop is required: We saw John last night, it was good to see him again. Although the meaning is clear, the use of a comma here is grammatically incorrect. A full stop or semicolon should be used.