Learn Russian: Твой аргумент убедительный, так как ты прав. - Your argument is convincing, since you are right.

Both mean "because" or "since", but так как is often translated as "since" or "as". It is slightly more formal and often presents a reason that is logical or already known to the listener. Another key difference is that you can start a sentence with так как, which you generally avoid doing with потому что.

Is the comma before так как mandatory?

Yes! In Russian grammar, you must always put a comma before a conjunction that introduces a new clause, such as так как, потому что, or что.

Why is убедительный in the long adjective form, but прав is in the short form?

The word прав (right/correct) is a special case and is almost exclusively used in its short form when describing people. For убедительный (convincing), the long form is very common in conversational Russian to describe a general trait. You could say Твой аргумент убедителен using the short form, but it would sound much more formal or literary.

How is the word убедительный formed?

It is built from the verb убедить (to convince). The suffix -тельн- is commonly used in Russian to turn verbs into adjectives, much like how English adds "-ing" or "-ive" to make words like "convincing" or "persuasive".