If one believes in cause and
effect then free will can not exist.
When we have multiple choices to
make a decision and we are free to choose any one we get the impression that we
have free will. But if we analyse the situation a bit more closely, we
understand that the process of choosing involves weighing several options
according to our previous samskaras, accumulated knowledge, responsibilites, interests etc
hence it is not free, but a deliberated decision.
If our deliberation tells us that
there is not much preference of one decision over the other, then we may pick
any one randomly in such case only we may see it was a free decision, but then
what is the advantage of a random decision ?
