Punctuation, compound sentence, Oxford, and [duplicate]

I've got myself confused with comma placement before the word 'and'.

I've read elsewhere on here that a comma should go before the word 'and' for compound sentences (this example was used, which I've borrowed, hope that's okay):

A cat can climb trees, and it can climb curtains.

[A cat can climb trees] + [A cat can climb curtains].

But how does this differ from a 'list', evoking the Oxford comma debate probably about using a comma in a list form, e.g.: a cat can climb trees, curtains and humans. Why is the above feline example not also considered a 'list'.

Here's another example - is this a compound sentence or a list or both? I assume it's a compound sentence, but it could be considered to be listing actions that they intend to do.

EXAMPLE We’re risk assessing every person on a case by case basis and we’re deciding what further treatment is required.

Have I got myself unnecessarily confused?!

Solution 1:

You use ",and" in compound sentences (Although this is not necessary for less wordy compound sentences). A compound sentence is composed of two independent clauses. An independent clause is generally composed of "subject + verb + object".

When you are listing something, you generally have one subject, one verb and multiple objects. Since the object does not count as an independent clause, it does not necessitate a ",and".

E.g. "A cat can climb trees, and it can climb curtains."

A cat [subject] can climb [verb] trees [object] {Independent clause}, and it [subject] can climb [verb] curtains [object] {Independent clause} = There are two independent clauses here.

However, if the sentence reads: "A cat can climb trees, curtains and people."

A cat [subject] can climb [verb] trees [object], curtains [object] and people [object].

There is only one subject and one verb; therefore only one independent clause.

Hope this helps.