Yes, no, adverbs, and interjections
There appears to be some disagreement over what function yes and no perform in the following sentences:
- Yes, you are right.
- No, you are mistaken.
According to ODO (yes, no), they are being used as exclamations which are presumably the same as interjections. Webster (yes, no) and Macmillan (yes, no), on the other hand, reckon that they are adverbs. Wiktionary (yes, no) chucks another spanner by stating that yes is being used as an adverb while no is being used as an interjection.
Wiktionary also links to a Wikipedia article on "yes and no" which seemingly disagrees with both options.
The words yes and no are not easily classified into any of the eight conventional parts of speech. Although sometimes classified as interjections, they do not qualify as such, and they are not adverbs. They are sometimes classified as a part of speech in their own right, sentence words, word sentences, or pro-sentences, although that category contains more than yes and no and not all linguists include them in their lists of sentence words. Sentences consisting solely of one of these two words are classified as minor sentences.
So, which, if anything, is it and why is opinion so divided?
I had a discussion about this recently. We all agreed that Yes and No were minor sentences when used this way. We also hit Wikipedia trying to decide - plus we're not linguists, so its not like our decision was authoritative. But here's our reasoning:
Definition: "A Minor Sentence is one that does not necessarily have a main verb in it, but which can be understood as a complete unit of meaning." When used as you do in your examples, the minor sentence becomes part of a compound sentence.
We went back and forth on a few of the listed other choices, and decided that adverbs were out since Yes isn't modifying the verb directly, and interjections were only valid if the Yes or No was used as a response such as:
Person A: "I've just secured us two tickets to the basketball game tonight."
Person B: "Yes!" (indicating excitement).
As to why opinions are divided, well... English is a bit of an anarchical language. It seems to be human nature that unless there's an established set or rules or an authority to base your arguments on it's hard to convince people to come to agreement.