How did the decipherment of Hittite support Ferdinand de Saussure’s hypothesis?

In 1879, linguist Ferdinand de Saussure hypothesized the existence of "laryngeal" consonants in Proto-Indo-European to explain vowel alternations and irregularities that could not be accounted for by the known vowel system. Because these sounds had largely disappeared or merged with other phonemes in most recorded Indo-European languages, his theory was initially met with skepticism.123

The decipherment of the Hittite language in the early 20th century provided the empirical evidence needed to validate his hypothesis. In 1927, linguist Jerzy Kuryłowicz demonstrated that Hittite preserved these reconstructed laryngeals in the form of a consonant written as h or hh (a guttural or pharyngeal fricative). By showing that Hittite contained these sounds in the exact positions where Saussure had theoretically posited them, the discovery confirmed the structural accuracy of Saussure’s model and solidified the modern understanding of the Proto-Indo-European phonological system.213