The book contains the most valuable materials from the scientific heritage of Solomon Davidovich Katsnelson (1907-1985), an outstanding theoretical linguist, one of the classics of Russian linguistics. The content of the book is the theory, methodology and history of the study of language forms and categories in their relation to categories of thinking. This edition includes incomplete monographs, as well as articles, essays and sketches. It presents what the author was preparing for publication, but did not have time to complete, and what was not intended for publication was written "for himself" as "notes for the future." The materials collected in this book from the archive of S. D. Katsnelson significantly complement previously published works, more fully reveal the topic of the relationship between the categories of language and thinking, which Solomon Davidovich has been developing for half a century. The publication of this book became possible thanks to the efforts of L. Yu. Braude, who carefully preserved and systematized the manuscript heritage of S. D. Katznelson.