Feature Value Switch
A feature switch toggles the features values on inherent lexical features. Assuming that nouns inherently possess Gender, Noun Class, and Number features, and that these features have several possible value settings, the lexicon must possess a mechanism for changing these values. Agentive nouns, for example, are regularly Masculine in IE languages but are capable of feminine as well as masculine reference. For example, it is possible for the noun student to refer to males and females in Russian. The Feminine correlate, student-k(a), however, refers exclusively to females.
If we assume that the Masculine form of such nouns has the feature settings [+Feminine, +Masculine], Russian requires a feature value switch which toggles this setting to [+Feminine, -Masculine] in order to fully semantically specify Feminine correlates. Notice that this characterization also fits nouns which are exclusively Feminine, which are not susceptible to derivation, such as sestra 'sister', mat' 'mother. It also predicts a class of exclusively Masculine nouns, [-Feminine, +Masculine]. Such nouns are found in the language, e.g. brat 'brother', otec 'father'. Interestingly, it also predicts a class of nouns which are neither Feminine nor Masculine but for whom Gender is relevant. This class is also found in Russian and other Slavic languages: tjulen' 'seal', sobaka 'dog', etc. are not specified for (Natural) Gender but are animate. Beard (1996) argues that these nouns have precisely this designation and, moreover, animacy is not a category in Slavic languages, but rather a peripheral function of Natural Gender.