Dagesh Chazak (‘Forte’) in the first letter of a word!
hine nna … vayomeru llo (Gen. 19:2) kumu tztze’u (ibid. v. 14)
A rule that has been passed down for hundreds of years states ‘When the letters Bet Gimel Dalet Kaf Peh Tav (Beged Kefet) occur at the beginning of a word, following a word ending with one of the letters Yud Heh Vav Alef (Yehu or Ehevi), the Beged Kefet letters are soft [fricative]; excepting [for four] cases where 1) the Yehu letter is pronounced as a consonant, 2) there is a pause [indicated by a major trope on the first of the two words], 3) the words press each other, 4) there is distance [between the trope].’  The exceptions are referred to in the literature as mevatelin (‘annulers’ – of the basic rule).  The meaning of mevatelin 3) and 4) is subject to dispute.     

The rule is quoted by Radak (Michlol, Lyck edition, folio 80), by Ramchal (Sefer haDikduk, shaar 3 chelek 6), and by others.  From the wording of the Masora (Daniel, Ch. 5) it seems that the rule was part of the Masora at one time.  Indeed, the language of the rule is the language of the Masora.  R’ Sh. Davlitzki writes ‘this rule is quoted by all books on the Masora, but I have not yet found it in the Masora’ (Chok Yehu uMvatlav 1). 

The basic rule assumes that it is known that the default position is that the letters Beged Kefet have a Dagesh (Kal) at the beginning of a word.  Thus the rule making Beged Kefet letters soft after Yehu letters is itself an exception to a more basic rule.  However R’ Davlitzki points out that the softening rule is broader than its literal sense.  Thus there are words that conclude with a long vowel creating a virtual Yehu ending (ibid).   Stated simply the rule means that a Beged Kefet letter is soft, if it comes at the beginning of a word following a word that ends in a long vowel.  In terms of articulation we can say that when pronouncing a vowel the vocal tract is open, so it is more convenient to follow it with a fricative consonant (which does not require total closure) than a plosive consonant (which does).

The first two mevatelin are self-explanatory: 1) means that if the Yehu letter does not indicate a long vowel but is rather a consonant in its own right, the softening effect does not occur, and the Dagesh is re-instated; 2) means that if there is a pause in diction between the two words, the effect of having just concluded articulating a vowel does not flow on, and again the Dagesh is re-instated.

Following Ramchal, 3) means that if the first word concludes with Heh and the preceding vowel is a Patach a Segol or a Kamatz, and one of the two words is short, and they are joined by a Makaf (‘hyphen’), then the Dagesh is re-instated; and 4) teaches that if the first word concludes with an actual Heh which is preceded by a Segol and there is only one vowel between the stressed syllable of the first word and that of the second, and the Heh is not of the root, the Dagesh is re-instated.  There are a number of other explanations.

In terms of articulation in the last two cases the two words are read as one, so the last syllable of the first word has a consonant after it (as is required for a short vowel) at the beginning of the following word!  That explains why R’ Chaim Kaslin in Maslul writes that when there is a Kamatz at the end of the first word (not following Ramchal) it is a Kamatz Katan (Maslul Netiv 13 Ot 100)!  According to this the Kamatz of hoshiah in hoshiah nna is a Kamatz Katan!  This is contrary to the living tradition of Sefaradi reading.

Ramchal notes that mevatelin 3) and 4) apply to all letters (other than the Gutturals and Resh).
We can now return to our original question.  Why a Dagesh in the Nun of nna in hine nna?  Exception 3) supplies the answer.  Why a Dagesh in the Lamed of llo in vayomeru llo and the Tzade of tztze’u in kumu tztze’u.  The rules cannot provide for this.  Minchat Shai here refers to the Masora (Daniel, Ch. 5) where these are listed as exceptions.

 *  *  *  * 

The meanings of words derived from Tzade Chet Kuf
yitzachak-li (Gen. 21:6) The verb is in the Kal conjugation and Rashi explains that it means ‘will rejoice with me’.
metzachek (Gen. 21:9) The verb is in the Pi’el conjugation and Rashi explains that it refers to idolatry, illicit relations, and murder.  We have here words from the same root with very different meanings and it would seem that this depends on the differing conjugations.  A check in a concordance reveals that the root Tzade Chet Kuf occurs in the Tenach only in Kal and Pi’el conjugations and in Kal it always connotes joy while in Pi’el it always connotes something derogatory.  Some people try to attach definite meanings to conjugations; these endeavors can easily mislead.  Ramchal writes that the Kal conjugation includes transitive and intransitive verbs.  About Pi’el he writes ‘mostly verbs which are intransitive in Kal are transitive in Pi’el. … Sometimes Pi’el verbs connote the lack of what the root itself connotes (Luzzatto, Sefer haDikduk Shaar 2 Chelek 2 Ch. 4).  Accordingly it may be that Tzade Chet Kuf in Pi’el connotes the lack of joy.