The origin of this science [i.e. logic] ... was as follows. Since in connection with philosophical matters there were many contrary opinions and thus many errors (because contraries are not true at the same time regarding the same thing), thoughtful people saw that this stemmed from a lack of training in reasoning, and that there could be no certainty in knowledge without training in reasoning. And so they studied the process of reasoning in order to reduce it to an art, and they established this science by means of which they completed and organised both this [science] itself and all others; and it is the science of the method of reasoning on all [subject] matters.Note that 'logic' in the medieval period covered more than formal logic, and covered metaphysics, semantics, informal and demonstrative reasoning as well. Nor did symbolic logic exist. Medieval logic is the logic of natural language, as ordinary people use it in argumentation.
*De ortu scientarum, ed. Albert G. Judy, London, The British Academy, 1976, chapter 53.