of gradation The consonant clusters and were, comprising two obstruents, not originally subject to gradation (as is still the case for similar clusters such as , , ). However, gradation pairs ht : *hð and hk : *hɣ were at one point introduced. The first of these patterns remains common in modern Finnish, e.g. vahti : vahdit ''. The second is only found in a limited number of words, e.g. pohje : pohkeet 'calf : calves', but rahka : rahkat ''. Usage varies for some words with , e.g. for the plural of nahka 'leather, hide', both nahat and nahkat are acceptable. Quantitative consonant gradation has expanded to include in addition to the pairs kk : k, pp : p, tt : t, also gg : g and bb : b (but not dd : d) in a number of recent loanwords, such as 'to blog'; 'to lobby'. Historical sound changes affecting conditions of gradation One important change was the loss of word-final *-k and *-h early on in the history of Finnish. This resulted in many open syllables with weak grades. In particular, the majority of nouns ending in -e are affected by this, with a weak grade in the nominative form. The imperative form of verbs also ended in a now-lost -k. For examples, side 'bandage', from *siðe, earlier *siðek (cf. Veps sideg, Eastern Votic sidõg); 'to get' → hae! 'get! (imp.)' from *haɣe, earlier *haɣek. Traces of the original syllable closure can be seen in sandhi effects: these classes of words can still be analyzed to contain the assimilative word-final 'consonant' ˣ, realized as lengthening of the next word's initial consonant. Therefore, hae side varastosta 'get a bandage from storage!' is pronounced , where the weak grades indeed occur in closed syllables. The loss of -k combined with loss of d gave rise to the modern Finnish infinitive ending, which was historically *-tak/täk. The final *-k triggered gradation, so that the ending normally became *-dak/däk. In turn, following the loss of d between unstressed vowels, and the loss of final *-k only *-aˣ/äˣ remained. Thus, (originally *) has only -a as the d was lost. But in verbs like juo-da 'to drink' the /d/ remained since it followed a stressed syllable. In the case of verbs like tulla 'to come', the earlier form was *tul-ðak, but the *ð was assimilated to the /l/ according to the patterns