40. T in the last syllable of a verb, preceded by a double vowel or l, n, r, changes to s before the i of the imperf., the vowels a, ä being suppressed. Thus from pyytää, to ask, comes pyysi (for pyytäi); from taitaa, can, taisi. But pitää, to hold, makes piti, because this vowel is simple.
Nousee, he arises, forms the imperfect nousi, but noutaa, he brings, makes nouti, to distinguish it from the other. Similarly kyntää, to plough, generally forms its imperfect kynti, to distinguish it from the same tense of kynsiä, to scratch.
In poetry forms like kielti, for kielsi, are found, and in the ordinary language a number of verbs which should by the above rule form the imperfect in si, either keep ti, as hoiti (hoitaa, to look after), jouti (joutaa, to have time), or have alternative forms, hääti or hääsi (häätää, to keep off), sääti or sääsi (säätää, to place), kiiti or kiisi (from kiitää, to hasten), hyyti or hyysi (hyytää, to freeze), syyti or syysi (syytää, throw out), sieti or siesi (sietää, to bear), jäyti or jäysi (jäytää, to gnaw).
T always becomes s in the imperfect of contracted verbs, lupata, to promise, pres. lupaan, impf. lupasin.
The combination ts is pronounced in dialects as tt or ht; e.g. metsä, a forest, appears as mettä or mehtä.
41. K before t, d, n becomes h. E.g. from the root teke, whose final vowel is liable to be rejected, come tehtiin, tehdään, tehnen, and also tehkää.
42. But h before s becomes k. Thus the stems yhte, one, kahte, two, haahte, a ship, form the nominatives yksi, kaksi, haaksi, te becoming si by the rules previously given, and h changing to k.
43. In contracted words (v. page [18]) h, when left as a final letter, becomes s, t, or the aspiration. Stem vieraha, nominative vieras, for vierah; stem kevähä, nominative kevät, for kevähä; stem venehe, nominative veneʻ, for venehe.
Though the above rules are given as being convenient for grammatical purposes, there is no doubt that in all these cases h is a weakening of some other letter; indeed, there is reason to think it is never original in Finnish. Vieras represents an original vierasa, and the genitive vierasan is weakened into vierahan and vieraan. Similarly in yksi, yhden, the k is more primitive.