A reading of the etymologies suggested by Wiesław Boryś, both in lexica and in numerous articles, makes us realize in a particularly acute manner the incompatibility of our linguistic competence in the evaluation of the motivation relations of Old Polish derivatives. The problem that was put forward was illustrated on the basis of Old Polish noun derivatives with the prefix wą‑ ( wądół, wąwał, wątok), the nominal equivalent of the verbal vъn‑/* vъ‑ (the PIE *on before a consonant yielded ϙ). In the Old Polish material there are also numerous lexemes structured on the basis of the Proto‑Slavic * ‑ϙtr‑/ ‑ętr‑, preceded by the syllable‑onset wn‑, which indicated an internal location ( wnątrz, wnętrze, wnętrek, wnętrzny etc.). The Old Polish lexemes with wą‑ and wn‑+‑ ϙtr‑/ ‑ętr‑ that were described compel us to put forward a legitimate thesis that our ancestors perceived them in a different manner than the modern users of the Polish language, that they were aware of word‑formative divisibility. They perceived them as nouns which originated on the basis of prepositional expressions, therefore they should be classed under the following heading: Derivatives formed on the basis of expressions with the preposition w‑ / wn‑ / wą‑.