Foreword No one understands me! This complaint, often expressed to criticize the isolation of one's own consciousness from others, could long rely on support from philosophy, linguistics, social sciences, and even communication studies. Tracing back to Descartes' distinction between res extensa and res cogitans, significantly intensified by Leibniz, and reverently admired in Romanticism and Existentialism, the thesis of human monads, which must remain foreign to one another, has long been able to assert itself, especially in the directions of social sciences that make consciousness and its achievements the starting point of their social theory. The thesis that we can never truly understand the other is well-known under the name of the problem of intersubjectivity. For a long time, it was considered unsolvable.