Within the depth-psychology corpus and its adjacent scholarly traditions, ‘vowel’ surfaces not as a psychological category proper but as a semiotic and phonological marker whose structural significance carries implications for theories of language, consciousness, and meaning-making. The most sustained treatment appears in Benveniste’s Last Lectures, where he situates the vowel at the precise hinge between Semitic and Greek writing systems: in Semitic orthography, consonantal templates carry grammatical structure while vowels remain functionally subordinate and graphically optional; in Greek, the vowel achieves full graphic parity with the consonant, an innovation Benveniste reads as the precondition for a distinct semiotics of language. This structural argument resonates with broader questions about how writing systems encode — or suppress — the phonological substrate of speech. Beekes, working in etymological territory, attends to vowel variation, prothetic vowels, and alternation patterns as diagnostic of Pre-Greek substrate languages, treating the vowel as evidence of contact, adaptation, and deep historical layering. The Homeric dictionary material engages the vowel metrically and morphologically, as a quantity governed by prosodic necessity. Benveniste’s account of Theuth recognizing vowels as a distinct class within the infinity of sounds gestures toward the cognitive act of phonological analysis itself — the vowel as the first object of linguistic self-consciousness. Across these registers, the vowel functions less as a psychological term than as a structural hinge between sound, script, and the organization of thought.