Both -ity and -ness are frequent and productive suffixes in English that fulfill the same core function: turning adjectives into nouns that denote the state or quality of whatever the adjective denotes. This well-known affix rivalry raises two core questions: 1. What determines the choice between -ity and -ness for a given base word? 2. Are the two affixes synonymous? For the first question, previous work has focused on morphological and phonological properties of the bases, but not their semantics. For question 2, the literature fails to give a convincing answer, with some studies, faced with doublets like ethnicity/ethnicness, arguing for a semantic difference, but most assuming synonymy. Using pretrained distributional vectors, I show empirically first that the semantics of the bases plays a major role in affix selection and second that the two affixes induce similar meaning shifts.
