Learn Finnish: Tämä uskomus lienee tarkoittanut sitä, että symboli on vaarallinen. - This belief probably meant that the symbol is dangerous.

Both are in the potential mood, which expresses probability. tarkoittanee is the present potential, meaning "probably means". lienee tarkoittanut is the perfect potential, formed with lienee (the potential form of olla) and the past participle tarkoittanut. It shifts the probability to the past, translating to "probably meant" or "has probably meant".

Why is the word sitä used right before the että clause?

The verb tarkoittaa usually requires its object to be in the partitive case. Because an entire että clause cannot be put into a grammatical case, Finnish often uses the partitive pronoun sitä as a placeholder object in the main clause to satisfy the verb's requirement.

In English we often say "meant that the symbol was dangerous". Why does the Finnish use the present tense on here?

English uses "backshifting" in reported speech or thoughts, changing "is" to "was" to match the past tense of the main verb. Finnish usually keeps the tense of the original statement or general truth. Since the original belief was "the symbol is dangerous", the subordinate clause stays in the present tense with on.

How does the word uskomus differ from usko?