The paper presents a language of thought (a set of cognitive units and relations) used to provide non-verbal definitions for the following five concepts: ARMCHAIR, MUG, RAVINE, LAKE, TREE. These definitions make it possible to describe concepts on two levels of specificity. On the first level, a concept is presented as a holistic cognitive unit. On the second, more specific, level, the same concept is viewed as a partitive system, i.e. a hierarchical system of its parts, the latter being smaller concepts into which the original holistic unit is decomposed. A hypothesis is advanced that such structure is inherent to all visible objects. The partitive system is argued to play a major role in human cognition. It, first, provides for an in-depth understanding of the perceived objects through understanding the role of their parts, and, second, underlies the formation of the hierarchy of concepts with respect to their generality. Besides, it can be considered as one of the defining properties of the human species as it accounts for the human ability to purposefully change the world.