 If linguistic signs no longer function as instruments for communicating independently existing thoughts and ideas from one mind to another, as Descartes, his followers and the empiricists believed, this raises the question of how individuals can communicate with each other through language, a question that becomes even more urgent if, as Humboldt maintained, states of consciousness cannot be transmitted from one individual to another at all, for “there can be nothing in our mind than that which is the result of its own activity” (eigne Thätigkeit) (GS Vol 5: 382). However, any communication between individuals presupposes a shared foundation: “We understand the word we hear only, because we could have said it ourselves” (GS Vol 5: 382). The words we hear and those that we utter are the stimuli for our language capacity to generate participatory responses. However, shared language capacity and linguistic competence cannot guarantee that one individual understands what the other is saying. Only through dialogue with the other can they test their understanding, amend and correct it, if necessary. Every understanding is therefore also a non-understanding, Humboldt argued. Thinking, in other words, is by its very nature tied to man’s social existence which means that it requires “a Thou that corresponds to the I”. A concept, Humboldt argued, can attain its distinctness and clarity only through its being reflected back from the intellect of another person (einer fremden Denkkraft, GS Vol 5: 380) with language as the only mediator between one intellect and another. At this point it becomes evident how radically Humboldt’s linguistic philosophy and his language studies part company with the traditional Cartesian way of understanding language. There existed for him a communicative prototype of human speech that is embedded in the structure of language itself manifesting itself in the different languages. This “prototype of all language” (Urtypus aller Sprachen) finds expression through the personal pronoun, that is, by the differentiation between the second and the third person. All speech is directed at someone and its structure cannot be understood by applying Cartesian grammatical analysis to it, because from a logical and grammatical point of view, it makes no difference whether I use the first, second or third personal pronoun, when in each case these pronouns function as the subject of a sentence. But for Humboldt I and he really are different entities, and with them, he argued, all possibilities are exhausted: because they constitute the I and the not-I. Thou is also a not I but unlike he, not in the “sphere of all beings”, but rather in another sphere of common action and interaction. In his empirical investigations Humboldt therefore paid special attention to the system of personal pronouns in a given language because it was from there that one could reconstruct the specific manifestation of the prototypal speech situation. Following this line of research in his Academy addresses “On the Dual Form” (1827) and “On the Relationship of the Adverbs of Place with the Pronoun in some Languages” (1829) Humboldt analyzed several dozen languages of different language groups from around the globe. It is in these texts that the marriage of philosophy of language and empirical linguistics that characterizes his work, can best be studied. 