Input-induced inter-speaker variation: evidence from Thai, Chinese and Japanese quantifier-negation sentences

• Identifies interspeaker variation in Thai all-not sentence interpretation. • Corpus study shows variation is not due to lack of input, contra prior claims. • Thai variation likely stems from rare inverse scope readings in the input. • Japanese corpus has more inverse readings; Chinese corpus has none. • Suggests interspeaker variation in Thai may result from the input. This study investigates inter-speaker variation in the interpretation of Quantifier–Negation (Q-Neg) sentences in Thai, with comparative evidence from Japanese and Chinese. Challenging the view that such variation stems from a lack of cues in the input, this research proposes an input-based account: variation arises from differences in the frequency of relevant cues available to individual speakers. A truth-value judgment experiment with 35 native Thai speakers revealed two distinct groups: one that accepts the inverse scope reading in Q-Neg sentences and one that rejects it. Cross-linguistic comparison shows that Japanese readily allows inverse scope readings, Chinese strictly prohibits them, and Thai falls in between, exhibiting speaker-dependent variation. A follow-up corpus study demonstrated that while Thai Q-Neg sentences are not rare, instances supporting the inverse scope reading are extremely limited. These findings support an input-based explanation: the inter-speaker variation observed among native Thai speakers arises from differences in input rather than from an absence of cues.