# What is it meant by a “hybrid argument”?

Can anyone explain (or point to a reference for) what a hybrid argument is in a security proof, and when it's convenient or preferable to use it?

Among some of the places where I've seen it mentioned, there is the paper Boneh, Sahai, Waters - Functional Encryption: Definitions and Challenges. The term standard hybrid argument is mentioned in the proof sketch of Theorem 1 within section 4.1.

The hybrid argument allows one to relate the distinguishability of a distribution (from uniform) to the predictability of individual bits given a prefix. The argument incurs a loss of a factor $k$ equal to the bit-length of the distributions: $\epsilon$-distinguishability implies $\epsilon/k$-predictability.