System complexity and (im)possible sound changes

In the acquisition of phonological patterns, learners tend to considerably reduce the complexity of their input. This learning bias may also constrain the set of possible sound changes, which might be expected to contain only those changes that do not increase the complexity of the system. However, sound change obviously involves more than just pattern learning. This paper investigates the role that inductive biases play by assessing the differences in system complexity of a small number of attested sound changes: the evolution of the obstruent and vowel inventories from Old English to Modern English, and the First Germanic Consonant Shift.