Although I do believe that cause and effect is a law of the universe, (demonstrated by the myriad of events we’ve been able to explain by determining their causes), I believe that it is still fundamentally a theory, because without complete knowledge of the universe and an understanding of all the inner workings of its tiniest particles it can still be argued that there isn’t in fact a cause for every effect which could support either indeterminism or libertarianism. Indeterminism more or less involves phenomena like chance and randomness. To believe in determinism is to believe that all cases of seeming randomness are simply cases of ignorance.
Consider games of chance. If there is a cause for every effect then there can be no chance. If a dice is rolled and lands on a four then there must be a reason or series of reasons for why the dice landed on a four. However, the reasons are so subtle that the roll of the dice is unpredictable. For example, as far as I know, one cannot mimic exactly how one throws a dice. They would have to control how exactly the dice is released from the hand and how hard the dice is thrown from the hand. What kind of material the dice landed on would also play a part in which side the dice landed on. Unpredictability is not the same as randomness though. It is just seeming randomness.