  Large language models (LLMs) have recently reached an impressive level of
linguistic capability, prompting comparisons with human language skills.
However, there have been relatively few systematic inquiries into the
linguistic capabilities of the latest generation of LLMs, and those studies
that do exist (i) ignore the remarkable ability of humans to generalize, (ii)
focus only on English, and (iii) investigate syntax or semantics and overlook
other capabilities that lie at the heart of human language, like morphology.
Here, we close these gaps by conducting the first rigorous analysis of the
morphological capabilities of ChatGPT in four typologically varied languages
(specifically, English, German, Tamil, and Turkish). We apply a version of
Berko's (1958) wug test to ChatGPT, using novel, uncontaminated datasets for
the four examined languages. We find that ChatGPT massively underperforms
purpose-built systems, particularly in English. Overall, our results -- through
the lens of morphology -- cast a new light on the linguistic capabilities of
ChatGPT, suggesting that claims of human-like language skills are premature and
misleading.
