"Feature neutrality" is an issue that has received much attention among linguists. For example, consider the sentence, "I have never, and will never, put my name on this document." Here, the verb 'put' acts simultaneously as a past participle (as in "have never put") and a base form (as in "will never put"), and is therefore said to be neutral between the two forms. Similar examples have been found for many languages.
The accepted wisdom is that neutrality is possible only for morphosyntactic features such as verb form, gender, number, declension class-not at the level of gross syntactic...