The author's interest focuses on the issue of paradoxical effects of using negations in directives (orders, suggestions, requests). First he refers to the speech acts theory to describe basic kinds of using negation in colloquial speech: negation in representatives, performative negation and negation in directives. The experiment refers to the impact of negated commands on giving attention to the object and, as a result, on remembering of the former which had differently formulated instructions. The results obtained indicate to the paradox of negated commands; the negated command brought about significantly greater attention focus to the given object than in the controlled conditions and similarly great attention focus like in the group which received the directly formulated suggestion, that is the suggestion to pay attention. In the discussion of the results of the experiment the author refers to the linguistic competence and speech acts theory.