The pair together may be either.
Than is a preposition. It isn't used to join two statements that could each be a sentence in their own rights. Rather is an adverb that must be followed by than; it says that it would be preferable for you to do the first option than the second and has the same effect when put before rather as when put after the verb. So rather than followed by a noun can be a preposition meaning "instead of" (e.g. potatoes rather than rice, stayed rather than going home).
However, the pair "rather than" can also connect an infinitive clause (rather than a gerund), acting as a conjunction as in the example,
"Rather than continue the argument, he walked away."
No, it is a conjunction, or less defintively a preposition. The similar word "then" can be an adverb.
No, it is not a conjunction. It is a preposition, or an adverb when no object is specified.
Yes, it is considered a conjunction used to compare the qualities of nouns (e.g. Bob is taller than Bill). But it might also be considered a preposition where only an object follows it.
"Since" may be used as a conjunction. It can also be an adverb and a preposition.
No. For is a preposition, or more rarely a conjunction.
When can you use than as a preposition rather than a conjunction?
Yes, it is a preposition. It can also be used as a conjunction.
No. Ordinarily rather is an adverb. (somewhat, or preferably) But it can pair with the conjunction "than" to create a preposition pair meaning "instead of" (potatoes rather than rice) and a conjunction pair that is used for negation, e..g. I decided to sleep late rather than be tired all day.
"Rather" is not a preposition; it is commonly used as an adverb to indicate preference or degree, and can also function as a conjunction or as a modifier.
If is not a preposition. It is a conjunction.
Who is a pronoun or a conjunction for restrictive clauses. It is not a preposition.
Yes, it is usually a conjunction (often as except for), but can also be a preposition.It can also rarely be a verb (to exclude).
"Or" is not a preposition. It's a conjunction.
No, but it can be a subordinating conjunction in sentences such as "There are more stars in the universe than there are grains of sand on your local beach."Other times, used in parallel construction, than acts more like a preposition: "He is taller than her brother" rather than "He is taller than she is."
B Than is not a preposition. It is a conjunction used to make comparisons.
Of is a preposition.
"for" can function as both a preposition and a conjunction. As a preposition, it shows a relationship between a noun or pronoun and other words in a sentence. As a conjunction, it connects words, phrases, or clauses.