The threefold division noun-verb-adjective is often considered a hallmark of the IE family from the remote PIE phase. However, Alfieri (2016, 2018, forth.) claims that this view is incorrect: while in Latin three major classes of lexemes are found (nouns, verbs and adjectives), in the Sanskrit language of the Rig Veda only two major classes are found (verbal roots and nouns) and the most typical “adjective” (i.e. the Quality Modifier) is a derived stem built on a verbal root meaning a quality. As a consequence, a deep and previously neglected typological change should be reconstructed in the IE family, namely the lexicalization of the adjective class and the change from a parts of speech (PoS) system “without” adjectives and quality concepts verbally encoded, which is still preserved in the RV, to a PoS system with “true” adjectives, which is found in Latin and in almost all other, especially modern and Western, IE languages. In this case, the data in Alfieri (2016, 2018, forth.) are confirmed focusing on the Quality Argument and the Quality Predicate, so as to show that the presence of a lexical class of adjectives is a common development that has come about independently in different branches of the IE family.