EN
The principal aim of this paper is to investigate the first uses of the metaphor of sleep and dream. This leads first to the general conclusion that the origins of the metaphor are to be looked for in philosophical texts, namely of Heraclitus and Plato. In the writings of the former it is related to the specific concept of the nature of man, characterized by unification and centralization - new in the period - of the cognitive functions. Heraclitus is apparently the first who uses the image of sleep to depict a state of cognitive or perceptive imperfection (basically an incapacity to see the reality), whereas Plato later establishes the similar use of the image of dream. In the course of the analysis more particular problem emerges, namely ambiguity related to the metaphor. In Heraclitus it is primarily the ambiguity due to his way of expression which invokes certain uncertainty whether the references to sleep found in the fragments are metaphorical at all. The conclusion is that this uncertainty is non-accidental and is to be connected to a more general ambiguity in Heraclitus writings concerning the question whether his perspective is normative or descriptive. Moreover, it is claimed in the paper that Heraclitus's lack of clarity corresponds to an even more general ambivalence with which Greek culture regarded sleep and dream in their literal sense and which appears much more clearly in Plato for whom (following Heraclitus) the metaphor of dream had not only a negative meaning but also a positive one (in the sense of pre-cognition). In the subsequent tradition, however, what primarily obtains is rather the negative meaning through which both authors together influenced the subsequent use of the metaphor, as seen, for example, in the case of Philo of Alexandria.