 Re: Coordinating conjunction in comma splices.
Yes, yet is usually classed as a co-ordinating conjunction, but is an odd one. It doesn't meet the rules for either subordinating conjunctions or sentence adverbials, so can't be classed with them, but on the other hand doesn't meet all the conditions for co-ordinating conjunctions either.
a) Why can't it be a subordinating conjunction?
Subordinating conjunctions, like although, are part of the clause they introduce. If the clauses swap position the subordinating conjunction moves:
He failed the exam, although he had studied really hard.
Although he had studied really hard, he failed the exam.
Co-ordinators like but, and and or can't do this. They have to stay in the middle of the two ideas. Yet is the same
He'd studied really hard, but he failed the exam.
He failed the exam, but he'd studied really hard.
He'd studied really hard, yet he failed the exam.
He failed the exam, yet he'd studied really hard.
b) Why can't it be a sentence adverb?
Sentence adverbs, like however, also come with the second idea, but they can be, and often are, separated from the rest of the clause by commas, and are flexible in position :
He studied very hard. However, he still failed the exam.
He studied very hard. He still, however, failed the exam.
He studied very hard. He still failed the exam, however.
You can't do that with co-ordinating conjunctions - they must come at the beginning of the second idea, whether they are in the same sentence or start a new one.
He had studied really hard. But/Yet he still failed the exam.
c) So why is "yet" different to the "pure" co-ordinating conjunctions??
So far yet has behaved identically to but. But there is one rule which but and and or follow that yet breaks - they can't combine with each other. I can, for example, combine a sentence adverb with a co-ordinating conjunction:
He studied really hard but still failed the exam, however.
and I can do the same with yet :
He studied really hard, but/and yet he failed the exam.
but I can't do it with but :
*He studied really hard and but he failed the exam. |