# Why is the state of a FSM traditionally denoted $q$?

While teaching how to implement FSMs using synchronous logical circuits, I noticed an intriguing coincidence: in both the theoretical CS world, and in the electrical engineering world, "state" is typically denoted $q$ (and the state space $Q$). I first asked on EE.sx, but then while researching a bit this topic, I found that even Turing's original 1936 paper uses $q_1..q_n$ to denote the states of the Turing machine.

So I wonder: When does this convention go back to, and why would a "state" be denoted $q$ ?

• If I had to guess, I'd say $q$ is short for "configuration" (because $c$ and $k$ are already bound to "constant"). But that's just a guess. – Jeffε Dec 21 '12 at 15:28
• this interesting question on the historical link between Turing machines and automata's top-voted answer denies there is a direct historical link between much automata theory and Turings 1936 paper. the bottom-voted answer points out the virtually identical similarity of the state table concept. – vzn Dec 21 '12 at 16:29
• I think you may get a better answer if you post it on MathOverflow. They have more computability theory experts. Another good place to ask this is FOM mailing list which has many experts on history of computability. – Kaveh Dec 24 '12 at 21:47