Speaking very roughly, fuzzy logic applies in cases where the degree of truth of a statement is in question. Logical uncertainty (about decidable sentences) applies in cases where the sentences are definitely true or false, but we lack the resources to figure out which.<p>So, for example, fuzzy logic might help you quantify to what extent someone is &quot;tall,&quot; where tallness admits of degrees rather than being binary. Or it might help you quantify to what extent a proof is &quot;long.&quot; But it won&#x27;t tell you how to calculate the subjective probability that there exists a proof of some theorem that is no more than 500 characters long in some fixed language. For that, you either need to find a proof, exhaustively demonstrate that no proof exists, or find a way to reason under logical uncertainty; and we haven&#x27;t found any ways to use fuzzy logic to make progress on formalizing inference under logical uncertainty.