It can be either.
As an adverb - The car drove past.
As a preposition - The car drove past the house.
It can also be an adjective. e.g. He has left the house only once in the past month.
It can also be a noun. e.g. The town had much racial turmoil in the past.
Yes, past is a preposition. Passed is not though.
No, "afterward" is an adverb, not a preposition. It is used to indicate time in relation to a past event.
No. Hence is an adverb or a conjunction (meaning therefore). It cannot be a preposition.
No. The word "at" is a preposition. Some archaic constructions (go at, have at) omit the object of the preposition.
The word "join" is not a preposition. It is a verb, or more rarely a noun (type of weld).
Yes, past is a preposition. Passed is not though.
No, "afterward" is an adverb, not a preposition. It is used to indicate time in relation to a past event.
On can be a preposition, adverb and adjective and so doesn't have a past tense. Only verbs have tenses.
No. Hence is an adverb or a conjunction (meaning therefore). It cannot be a preposition.
No. The word "at" is a preposition. Some archaic constructions (go at, have at) omit the object of the preposition.
Through is not a verb so it doesn't have a past or present form, it is a preposition or adverb or adjective.
Yes, the noun past is a common, singular, abstract noun. The word past is also an adjective, an adverb, and a preposition.
No, it is not a preposition. Tall is an adjective and possibly an adverb.
Yes, the noun past is a common, singular, abstract noun. The word past is also an adjective, an adverb, and a preposition.
The word "join" is not a preposition. It is a verb, or more rarely a noun (type of weld).
It is never an adverb. It is always a preposition. The word "within" can be an adverb or a preposition, and the word "forthwith" (immediately) is an adverb.
It is never an adverb. It is always a preposition. The word "within" can be an adverb or a preposition, and the word "forthwith" (immediately) is an adverb.