Abstract: How many possibilities we have to say the truth about the physical reality? I think that it is one of the most interesting questions in the XXI century. Scientists use words like ‘possible worlds’, ‘parallel universes’ and ‘multiverse’. The threshold of knowledge in physical sciences seems to go to a new statute: the probable, like a border which not divide the absolute truth by the contingency of reality, but represent the interlude between the mathematical and geometrical world and factual truth. This idea was addressed in the philosophy of XVII century. We can found in Leibniz’s thoughts a particular vision about the Truth. He formulated the famous distinction between Truths of Reason and Truth of Fact. The first are eternal elements and they are caused by themselves, they are characterized by absolute necessity. The elements of factual reality are corruptible and prone to changes, they are characterized by hypothetical necessity. The only way to say the truth in factual reality is to deplete all of substance attributes, but it is impossible. The mathematic and geometric application on reality is not enough for a perfect knowledge of human and physical events. I think that in the Leibniz’s philosophy we can stipulate a threshold of Probable that represents the current touch point between the mathematical truth and the limit of empirical observations.