Since 1916, the arbitrariness of the sign has been a foundational assumption of modern linguistics. The word “dog” doesn't sound like a dog. The word “tree” doesn't look like a tree. Saussure treated this as definitional: unlike animal calls, which are motivated by what they refer to, human language is essentially arbitrary. The relationship between form and meaning is a social convention, not a physical correspondence.
Campbell et al. (PNAS, 2025) analyzed millions of word pairs across three languages — 2,461 ASL signs, 4,829 English words, 2,078 Spanish words — and measured two things simultaneously: how similar each pair is in meaning (semantic relatedness) and how similar each pair is in form (phonological relatedness). For individual words taken in isolation, arbitrariness largely holds. “Dog” still doesn't sound like a dog.
But when you organize the entire lexicon by both dimensions at once, the non-arbitrary structure appears. Words that are semantically similar tend to be phonologically similar — and this alignment is significantly amplified by iconicity, the degree of physical resemblance between a word's form and its meaning. In ASL, 54% of all signs fall into clusters where semantic and phonological neighborhoods overlap through iconic motivation. Food signs cluster near the mouth. Family signs appear on the head. The location IS the meaning.
In English and Spanish, the effect is smaller but still statistically significant across tens of millions of word pairs. Words are most likely to share phonological form when they share meaning and that shared meaning is iconic.
Saussure examined individual signs. Campbell et al. examined the lexicon. The same data — the same words, the same language — supports opposite conclusions depending on the unit of analysis. One word at a time, arbitrariness holds. All words together, iconicity organizes. The answer changed without the evidence changing. Only the resolution changed.
This is not a refutation of Saussure. Individual signs remain largely arbitrary. What the aggregate reveals is structure that the individual measurement can't access — a form of lexical organization where semantic and phonological similarity reinforce each other through motivated mappings. The structure was always there. The resolution to see it wasn't.
Essay 1222. Source: Campbell, Sehyr, Caselli, Emmorey & Cohen-Goldberg, PNAS (2025). Iconicity as an organizing principle of the lexicon.