Here’s an excerpt from Zabarella’s Opera Logica:
For all scientific advance from the known to the unknown is either from a cause to an effect or from an effect to a cause. The former indeed is the demonstrative method; but the latter is the resolutive method. There is no other process that brings forth certain knowledge of a thing. For if we advance from something to something else, neither of which is the cause of the other, it is not possible for there to be an essential or necessary connection between them. Hence, no certain cognition can follow from the advance. Therefore, it follows that there is no scientific method besides the demonstrative and resolutive ones.