поскольку vs так как
poskol'ku vs tak kak — since/because vs because/as
Register: neutral / formal
What it really means
Поскольку and так как both introduce causal subordinate clauses. Поскольку is especially useful for a known or background reason and often comes first in formal exposition. Так как is more direct and conversational; when the clause follows the main clause, comma placement separates the causal clause.
Examples in natural speech
Поскольку было поздно, мы ушли.
Since it was late, we left.
Он молчал, поскольку не знал ответа.
He stayed silent because he did not know the answer.
Так как шёл дождь, матч отменили.
Because it was raining, the match was cancelled.
Я остался дома, так как заболел.
I stayed home because I got ill.
Поскольку документы готовы, можно начинать.
Since the documents are ready, we can begin.
Common mistakes
Do not write поскольку as two words. Both conjunctions introduce clauses, not a bare noun; use из-за/по причине for nouns. Keep the comma at the clause boundary, especially when the causal clause comes first.
Memory tip
Поскольку sets the background; так как gives the plain spoken reason.
Frequently asked questions
Does поскольку always mean “since” in time?
No, it normally means causal “since/because”; temporal since is usually «с тех пор как».
Is поскольку more formal?
It is somewhat more bookish and logical in tone, while так как is extremely common in ordinary speech.
Can поскольку be placed after the main clause?
Yes: «Мы ушли, поскольку было поздно» is grammatical and states the reason afterward.
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