Reasoning: In black & white?

This paper is just devoted to introduce a mathematical model unifying the reasonings that are comprehended under the labels `deduction´, `refutation´, `abduction´, and `induction´. Such model can be summarized by the expression `conjecturing and refuting´, comes from the work the author did from the year 2000, and basically tries to represent a good deal of Commonsense Reasoning representable by fuzzy sets. In such model conjectures are understood as consisting in weak and strong consequences, hypotheses, and speculations. The model is presented for submitting it to philosophical reflection.