A Symbolic Analysis of Relay and Switching Circuits

Shannon was 21 and running Vannevar Bush's differential analyzer at MIT, a machine whose control circuits were several hundred relays wired up by experience and rule of thumb. He had read Boole during a summer course in Michigan and spotted the correspondence: two relays in series are AND, two in parallel are OR, a normally-closed contact is NOT. A switching network can therefore be written as an algebraic expression, the expression can be simplified, and the simplified form is a cheaper circuit.

Submitted in 1937, published in the Transactions of the AIEE the following year, and awarded the Alfred Noble Prize in 1939. The consequence was that telephone engineering stopped being a craft and became a discipline with proofs: anyone who later built a relay computer could know the circuit was correct before soldering it. It is routinely called the most important master's thesis of the century, a claim that is hard to argue with and easy to overlook — Shannon went on to found information theory eleven years later, and that is the achievement people remember.