What does the superscript x in Finnish IPA mean?

Question

IPA transcriptions like /muːtːuɑˣ/ from here show a superscripted x. The Finnish Phonology Wiki page says, in the Sandhi section:

Gemination of a morpheme-initial consonant occurs when the morpheme preceding it ends in a vowel and belongs to one of certain morphological classes. Gemination or a tendency of a morpheme to cause gemination is sometimes indicated with an apostrophe or a superscripted "x", e.g. vene /ʋeneˣ/. Examples of gemination:

I know that gemination is basically consonant lengthening, like when you say "bad dream". But that sentence is a little over my head and couldn't find much else. So does the "x" make a sound, or what is happening here? Can you explain it in slightly simpler terms? Why do so many Finnish words have it in the IPA transcription?

Answer 1

Phonemes are theoretical units, which don't always map directly to sounds.

In this case, to my understanding, the phonologist behind this analysis has proposed that there's a special phoneme /ˣ/ which makes a following consonant geminate. For example, if hake "woodchips" is underlyingly /ˈhɑkeˣ/, that explains why hake-lava "woodchip-box" has a geminate [hɑkelːɑʋɑ], while lava "box" doesn't: the gemination reflects underlying /ˣl/.

Some analyses of Japanese posit something similar, with a phoneme /Q/ that lengthens a following consonant. In these analyses, /Q/ and /N/ are the only phonemes that can appear in a coda, and each get a mora of their own; a word like Nippon is phonemically something like /niQ.poN/.

Answer 2

This is a well-known problem of Finnish phonology, made widely known to the general linguistic audience in this article by Keyser & Kiparsky. There is no standard notation for indicating this property in Finnish – K&K don't give this a segmental transcription, instead they treat it as being "CV". I have seen it treat as h also k, which is possible since there is no competing word tervek or terveh that has to be distinguished. It's a Wikipedia-internal issue as to why that non-standard notation is used, and you would have to ask the "author" why they use this notation. Outside of Wikipedia, we understand this to be a diacritic referring to the fact that there used to be some consonant there, which affects the contemporary phonology of the language. It is sometimes called a "fleeting" consonant.

In his historical treatment of the development of Finnish, Hakulinen (1961) speaks of this property as being a "laryngeal stop", written as ', which derives historically from k, h, t and n, and he also notes that

In the pronunciation of modern Finnish the laryngeal stop is virtually non-existent. The mark ' used above and elsewhere in this book is a purely etymological sign with no phonetic value.