Having recognized the iconic and the arbitrary faces of sign, contemporary researchers from different fields converged on the significance of mimesis at earlier stages of the evolutionary trajectory. This dissertation investigates the presence of iconicity in Proto-Indo-European (PIE) roots. It combines the typological, historical and comparative perspectives to broaden the research of naturalness to historically older languages and shed light on how iconic devices mirror archaic concepts. It is especially advantageous to use the material of reconstructed systems, like PIE, which gave rise to a whole number of attested languages. Despite the fact that PIE is a hypothetical reconstruction, in this research it is treated as the preceding invariant of diversified branches forming a large family. With respect to iconicity, etymologies may elucidate the evolutionary role of isomorphism between cognitive and language structures, motivation and transparency between the code and the encoded concepts, the importance of imitation in semiogenesis. The purpose of this study is to find out about the relevance of the universal principle of iconicity to PIE and its manifestations in the parent language of the Indo-European family. What were the ways by which the structure of the PIE basic forms and its variants or modifications reflected structures in the external world and how they motivated the semantic continuants of PIE etymons in various daughter languages? The study is based on the following hypothesis: at earlier stages of language and culture evolution, language and thought were highly isomorphic. The principle of iconicity, both effective and efficient in sign-making processes, manifested in the structures of the PIE roots / stems motivated by the meanings they expressed. Etymological databases and dictionaries were used to select productive etymons out of 2044 Proto-Indo-European reconstructions. The selection was followed by a structural analysis of basic forms and their modifications. Next, the meanings of reflexes and their derivatives (extracted from lexicographic and literary sources) were analysed in order to further establish semantic similarities and dissimilarities between PIE basic forms and root modifications, and identify form-meaning correspondences in the etymons. Manipulations with phonetic and morphological structures of basic forms and variants turned out to be highly efficient at expressing intuitions and knowledge about fundamental properties of entities: their ability to extend, disintegrate, and continue, on the one hand, and their ability to shrink, accumulate, and integrate, on the other. Formal symmetry around the vocalic core (CVC) correlates with semantic syncretism and can be treated as an iconic representation of 'indivisible duality' or 'wholeness, cohesion', whereas the asymmetric (metathetically arranged) counterparts CCVC and CVCC mime two aspects or perspectives from which something can be considered. Such devices as qualitative and quantitative alternation, reduplication, and metathesis were exploited in PIE to mime perceivable (basic) discriminations: contrast and similarity, continuity and discontinuity, proximity and distance, openness and closure, and they resulted from an intrinsic ability to distinguish between figure and ground, between something more prominent and diffused.
