However, consider:Terra wrote:This is different. You are no longer joining 2 nouns, but 2 clauses."The man went therefore the woman went too."
Examples:
(Joining 2 nouns)
Good: The man and the woman are hungry.
Good: (Either) the man or the woman is hungry.
Bad: The man but the woman are/is hungry.
Bad: The man therefore the woman are/is hungry.
(Joining 2 clauses)
Good: The man is hungry, and the woman is thirsty.
Good: (Either) the man is hungry, or the the woman is thirsty.
Good: The man is hungry, but the woman is thirsty.
Good: The man is hungry, therefore the woman is thirsty.
"but" looks like it's the same PoS as "therefore", not "and" or "or". Furthermore, it doesn't make sense to label "and" and "or" as a single PoS. Instead, I would say that they can be one of two PoS depending on the situation.
I didn't see the man, but the woman. (NP conj NP)
*I didn't see the man, therefore the woman.
Worship no god but Allah.
*Worship no god therefore Allah.
He didn't fall off but was pushed. (VP conj VP)
*He didn't fall off therefore was pushed.
He loves me but not you. (NP conj NP)
?He loves me therefore not you.
I don't think "therefore" is a conjunction at all; as I said earlier, it fits into adverb slots.
"But" originally meant "without, outside", thus "except", so the usages like "Worship no god but Allah" (i.e. "except Allah") are the oldest sense, and are really prepositions. Perhaps the simplest explanation is that over centuries it's been moving from preposition to conjunction, but hasn't entirely arrived.