The original artificial neuron, the Pitts-McCulloch neuron, was a propositional logic circuit, conceived entirely on the basis of a model of biological neurons as logic gates, with a threshold function that controlled their true or false value. It was even called the Threshold Logic Unit. The paper where it was first described is titled "A Logical Calculus of the Ideas Immanent in Nervous Activity". In fact, the perceptron too was a logic circuit, a function with two outputs, "positive" and "negative ... or "true" and "false".

AI researchers always used the tools that all scientists use to model their subject, in this case, intelligence: maths. Logic is maths, just as probabilities, calculus, algebra, etc etc.