But joins on a member of this sentence which expresses, not only something added, but, also, opposition of meaning.
The principal conjunctions, may be known by the following lists, which you may now commit to memory. Some words in these lists, are, however, frequently used as adverbs, and sometimes as prepositions; but if you study well the nature of all the different sorts of words, you cannot be at a loss to tell the part of speech of any word in the language.
LISTS OF THE CONJUNCTIONS.
Copulative. And, if, that, both, then, since, for, because, therefore, wherefore, provided, besides.
Disjunctive. But, or, nor, as, than, lest, though, unless, either, neither, yet, notwithstanding, nevertheless, except, whether, whereas, as well as.
Some conjunctions are followed by corresponding conjunctions, so that, in the subsequent member of the sentence, the latter answers to the former; as,
1. Though—yet or nevertheless; as, "Though he was rich, yet for our sakes he became poor."
2. Whether—or; as, "Whether he will go, or not, I cannot tell." It is improper to say, "Whether he will go or no."
3. Either—or; as, "I will either send it, or bring it myself."
4. Neither—nor; as, "Neither thou nor I can comprehend it."