But and commas

[durianman]

Shopping is difficult, but it is fun to do.
Shopping is difficult, but fun to do.
In the second sentence does a subject need to be written out? Isn't it implied (an ellipsis)? Without the subject in the second clause it still needs a comma, right?
Yet with "and " as a coordinating conjuction this is not true.
I should not use a comma in the second phrase unless there is a subject and that subject must be written not implied

[Coffa]

Originally Posted by durianman

Shopping is difficult, but it is fun to do.
Shopping is difficult, but fun to do.
In the second sentence does a subject need to be written out? Isn't it implied (an ellipsis)? Without the subject in the second clause it still needs a comma, right?
Yet with "and " as a coordinating conjuction this is not true.
I should not use a comma in the second phrase unless there is a subject and that subject must be written not implied

The subject does not need to be written out - it is implied, as you correctly say. It also needs a comma, because there is a pause before 'but'.

A comma is a punctuation mark denoting a speech pause, and that is the only rule that applies - not whether you use a conjunction or not. For example:

1) "Working for a living is hard and boring."
2) "Working for a living is hard, and boring."

Both sentences are correct. In the first one, the conjunction is used to make a compound adjective - 'hard and boring'. In the second, the conjunction is used to connect the two phrases - it is a contraction of: "Working for a living is hard, and (it is) boring." This difference is indicated in speech by a pause in 2), and that is why the comma is used.