Whats the basic logic/thinking behind Baye's theorem in probability?


I have practiced questions on Bayes theorem,but sometimes I had confusion whether I have to use bayes theorem in the question or not.Whats the basic logic/intuition behind it?


The Real intuition is when the problem is about determining something. Like say , spam filters use Bayesian updating to determine whether an email is real or spam, given the words in the email. . So say x in given in Y . Now again you have determine whether , Y is not appearing or probability of Y. Hope it clears your doubt


that was of no help,i will better read wikipedia