The paper is on the role of complex thought in the development of thought and scientific knowledge. According to Vigotsky, the complex thought is the first phase in the ontogenesis and phylogenesis of human thought. It is in this sense pre-conceptual. Also, according to Vigotsky, the complex thought has its internal genesis which begins with associative complexes and ends in pseudo-concepts. Complex also an explanatory role in scientific thought. Complex thought ppears on all levels and stages of the development of scientific knowledge. Metaphors may appear in the complex thought as a dominant mode of thought or in the conceptual structure as the auxiliary in the explanation. Analogies present a certain structuration of the complex thought, which contributes to the creation of conceptual structure. The place of analogy is thus between a complex thought and conceptual thought.