Qualitate qua is a concise knowledge theory that relativizes and interweaves reality, language, man, and number into a simple and precise intersubjective fabric. The fabric is sufficiently precise for the purpose of design and even calculation. It is nevertheless so powerful that it offers unlimited space to multiform and liquid reality, living language, and subjective man. In an extensive introduction, the author justifies his work and describes the philosophical quest that has preceded it. The knowledge theory itself contains 21 paragraphs of two pages each, the form of which wishes to remind of Wittgenstein's Tractatus Logico-Philosophicus. Still, its contents are fundamentally different.