What is natural language processing NLP? A second category of structural generalization studies focuses on morphological inflection, a popular testing ground for questions about human structural generalization abilities. Most of this work considers i.i.d. train–test splits, but recent studies have focused on how morphological transducer models generalize across languages (for example, ref. 36) as well as within each language37. The last axis of our taxonomy considers the locus of the data shift, which describes between which of the data distributions…