The Russian language is in possession of a clitic -ka which functions as an intensifier when used with pronouns and adverbs, but as a softener when used with imperatives. Hypothetically, a sentence such as tut-ka daj-ka mne-ka otdoxnut′ ‘let me rest here’ could be produced exemplifying the workings of this particular clitic. However, the difference in meanings between -ka used with pronouns and adverbs, as opposed to -ka used with imperatives, strikes one as contradictory. Why on the one hand does -ka add a sense of intensification, while on the other it softens? I believe there is an historical explanation for this dichotomy. Synchronically we are dealing with a single clitic -ka, but diachronically we have two distinct clitics: -ka and -tko.
There is an intensifying clitic -ka known to all three branches of Slavic that is used with pronouns and adverbs in a consistently similar manner. There is also the imperative clitic -tko/ used by Archpriest Avvakum in the seventeenth century which had two allomorphs: post-vocalically he used [-tko], but post-consonantally [-ko]. Avvakum did not use -ka as an imperative clitic. But by the late nineteenth century the situation had changed. In 1871 A. F. Gil′ferding published a three-volume collection of byliny under the name Onežskie byliny. These Onega byliny are replete with instances of -ka used with pronouns and adverbs, but only rarely with imperatives. Of the fifty-one of Gil′ferding’s informants who provided enough tokens of the softening clitic to be conclusive, twenty demonstrated the same distribution as Avvakum: -tko was used post-vocalically, but -ko post-consonantally. However, five informants used only -ko regardless of the phonetic environment. The remaining twenty-six informants showed that a change was underway: the -ko allomorph was gradually spreading to the post-vocalic environment at the expense of -tko. Consequently, data from Avvakum and the Onega informants show that the imperative clitic in this okanie dialect was -tko or -ko (itself derived from -tko), not -ka.
The Onega byliny demonstrate yet another outstanding phenomenon with regards to the intensifying clitic -ka: although the imperative clitic is clearly -tko and, to a lesser extent, -ko, -ka is frequently encountered, though strictly as an intensifier of pronouns and adverbs. On the basis of this observation, I conclude that, although Standard Russian makes use of a single clitic -ka which has two seemingly contradictory meanings, the intensifying clitic used with pronouns and adverbs is etymologically distinct from the imperative clitic -tko (and -ko.
One Lake Onega informant, in addition to his use of -ko as the softening clitic, used the form -tka, which had two allomorphs: post-vocalically he used -tka, but post-consonantally he used -ka. Farther south in akanie dialects, the same clitic -tka appears with the same two allomorphs. This suggests that the softening clitic -tka of akanie dialects probably derives from -tko, only in akanie dialects the clitic came to be analyzed as having an underlying a. Consequently, I conclude that the etymology of the softening clitic -ka is twofold—although it is possible that speakers innovated by extending the intensifying clitic -ka to imperatives, in some instances speakers use a clitic -ka which ultimately derives from -tko (-tko > -tka > -ka). That is, a development took place in akanie dialects similar to the one in progress around Lake Onega in the late nineteenth century. That development is demonstrated by one Onega informant, but corroborated in data from neighboring dialects. Thus, the softening clitic -ka (of either origin) eventually suppleted -tko, -ko and -tka in most dialects leaving behind a semantic dichotomy.