'For' is a coordinating conjunction, but 'because' is a subordinating conjunction. Is that right? Can someone explain why?

Solution 1:

It's not surprising you're confused. There really isn't much difference in meaning between for and because here, but there's a difference in grammar, which is why for is traditionally classified as a coordinating conjunction and because as a subordinating conjunction.

The difference between subordinating conjunctions and coordinating conjunctions is the allowable word orders. Coordinating conjunctions have to come between the two phrases they are connecting, while there is no such requirement for subordinating conjunctions.

For example, you can say all of

He went to bed because he was tired,
He went to bed since he was tired,
He went to bed, for he was tired.

But if you try reversing the order of the clauses, only two of these conjunctions work. You can say:

Because he was tired, he went to bed,
Since he was tired, he went to bed,

but not

*For he was tired, he went to bed.

And that is why for is called a coordinating conjunction, while because and since are called subordinating conjunctions.

Solution 2:

In response to Peter Shor's comment: "And that is why for is a coordinating conjunction, while because and since are subordinating conjunctions".

With items like "since" / "before" / "after", they uncontroversially occur as prepositions when they have an NP as complement, and there's no basis for assigning them to different categories according as they take an NP or a clause -- or no complement at all. Trad grammar has:

since the meeting:............. [preposition + noun]

since we arrived:............... [subordinating conjunction + sub clause]

(I hadn't seen her) since:.. [adverb, no complement]

This is just a matter of varying complementation, which is commonplace. Compare verbs:

I know her father ............. [verb + NP]

I know that he's ill............ [verb + clause]

I know.............................. [verb without complement]

Or noun:

a belief in God ..................... [noun + PP]

the belief that God exists......[noun + clause]

her beliefs.............................[noun without complement]

We need therefore to distinguish "since" from the genuine subordinators "that/whether", and then once we've done that "since" clearly belongs with other prepositions.