The paper solves the problems connected with the occurrences of expressions in the de re or de dicto supposition. It is shown that some expressions, e.g. definite descriptions, that are seemingly ambiguous are in no way ambiguous, they denote in all the contexts one and the same “thing” and have a precise definite meaning which is best explicated by the TIL logical construction. What differs is only the supposition in which they occur. The precise definition of the distinction between de (...) re, de dicto occurrence is provided, and using this definition four kinds of problems are analysed, namely de re / de dicto using definite descriptions , sentences , definite descriptions in notional attitudes, and embedded sentences in propositional attitudes. The paper provides a certain adjustment and correction of Tichý’s approach to the problem. (shrink)