# Why is SAT not in P? [duplicate]

I'm studing P and NP complexity classes. I like know, why is SAT not in P? Is it because I can not determine if any Boolean expression is satisfiable?

• We don't know whether SAT$\notin$P or not, and we certainly don't have any idea why that would be true (other than geometric complexity theory). – Yuval Filmus Nov 8 '13 at 0:54
• Have you tried reading the Wikipedia articles about SAT and P vs. NP? – Kaveh Nov 8 '13 at 2:06
• Please read our reference question on this topic; I'm closing as duplicate since the answer to your (quite uninformed, to be honest) question is there. – Raphael Nov 8 '13 at 13:17

If there are $n$ variables, then we can try all $2^{n}$ possible truth assignments, and eventually we'll find if there is a satisfying one, but this is not polynomial time with respect to the size of the input.