[This is part of a series of defectivity case studies.]

Pertsova (2005, henceforth P) describes defectivity in the genitive plural (henceforth, gen.pl.) of Russian nouns. This defectivity is not quite as extensive as in the verbs: Zaliznyak’s (1977) renowned morphological dictionary, Pertsova’s primary source, labels roughly forty noun lexemes as Р.мн. затрудн. ‘gen.pl. difficult’ (P gives this as ‘awkward’), and a smaller number are labeled Р.мн. нет ‘gen.pl. does not exist’. Pre-theoretically, the Russian gen.pl. form has three complexities. First, there are three (surface) gen.pl. suffixes: -ej, -ov, and a null -∅ (though this is often taken to be the surface form of a back yer; e.g., Bailyn & Nevins 2008). Secondly, stress may either fall on the stem or the desinence, depending on a number of factors. First, the fleeting vowels found in many Slavic languages, sometimes surface in the final syllable of the stem of null gen.pl. forms; e.g., kiška ‘gut’ has a gen.pl kišok.

Let us consider the ‘do not exist’ cases first. A few examples are dno ‘bottom’, mgla ‘haze’, and mzda, an archaic word meaning ‘bribe’. All three of these are built from stems consisting solely of consonants—the -o and -a are nom.sg. affixes—and according to P, we would expect them to form a null gen.pl.¹ Were they do so, then, the gen.pl. form would be a purely consonantal sequence (*dn, *mgl, *mzd, etc.). While Russian allows quite rich onsets, it does not permit vowel-less prosodic words. So, presumably, these ‘do not exist’ cases are in some sense derived, but are unpronounceable.

The cases labeled by Zaliznyak as ‘difficult’ are perhaps more challenging. These include fata ‘veil’, yula ‘weasel’, and suma ‘bag, pouch’. Many of these (e.g., čalma ‘turban’, taxta ‘ottoman’, mulla ‘mullah’) are borrowings from Tatar or other Turkic languages. All forty ‘difficult’ nouns are all feminines in -a, and all of them have desinential stress (i.e., stress on the case/number suffix) throughout. According to P, these ‘difficult’ nouns would all have a null gen.pl. were it not ineffable. This means that stem stress is the only option (because duh, there’s no way to stress a null desinence). Yet speakers are reluctant to introduce a new, stem-stressed allomorph of the stem that does not otherwise exhibit stem stress, because of a principle known as lexical conservatism.

I follow this basic logic, but I am not sure how to make the lexical conservatism filter into something mechanistic and appropriately parameterized so that it can actually predict the data we observe. P points out that there are other nouns which have exactly the same properties (null gen.pl., desinential stress) but resolve this conflict by retracting stress to the final syllable of the stem. For example, borodá ‘beard’ has a null, stem-stressed, but unobjectionable gen.pl. boród, as does the previously mentioned kišká/kišók.² After considering and rejecting an appeal to frequency, P suggests that there is something special about monosyllabic stems that makes them more resistent to stem allomorphy. The problems do not end here, because as P gamely points out, the gen.pl. is not the only case/number combination which forces stress retraction; it also happens in the null nom.sg. of masculines like stol ‘table’, but I am aware of any Russian nouns which are defective in the nom.sg.

While I find P’s description clear, I do not think her analysis works. It correctly identifies two interesting explananda—the fact that gaps are localized to monosyllabic stems, and to the genitive plurals—but gives little explanation for these facts. And the invocation of lexical conservatism, never that well-defined in the first place, has done little to help; it could just as well be that the conflict between desinential stress and the selection of a null gen.pl. produces ineffability. Lexical conservatism actually prevents us from uniting the ‘does not exist’ and the ‘difficult’ cases, which after all both involve monosyllabic stems expected to exhibit desinential stress and a null gen.pl.³

Sims (2015) notes that these defective nouns might be an interesting case for studying the interaction between defectivity and syncretism, a topic first discussed by Stump (2010). In Russian there is syncretism between gen.pl. and accusative plural (acc.pl.) forms for all animate nouns. Since twelve of the defective nouns are animates, this  means that either there is an exception to this syncretism (in the case that the acc.pl. is acceptable) or perhaps, the defectivity itself is carried over by the syncretism and nouns are defective in the acc.pl. too. No one seems to have gathered the relevant judgments  about the well-formedness of these animates in their gen.pl. vs. acc.pl. forms yet.

Postscript

As is also the case for Russian verbs, defectivity in Russian nouns has arguably risen to the level of conscious awareness among Russophones. In his short story Kocherga, the Soviet humorist Mikhail Zoshchenko tells of workers who wish to order five more fire pokers for their drafty office. The nom.sg. kocherga ‘fire poker’, is unobjectionable, but no one they talk to is sure what the gen.pl., the case used for five or more of an object in a quantified noun phrase like ‘five fire pokers’, ought to be, and both they and their interlocutors use clever circumlocutions to dodge the question.

Endnotes

1. I note that Wiktionary gives the gen.pl. of dno as don’ev, with a back stem yer  surfacing (also bearing stress) and the -ev gen.pl. suffix. If this is correct, this is a problem for P’s claim that stems of this class are expected to have a null gen.pl., unless there is some other reason dno to behaves differently than mgla or mzda.
2. Here I am using acute accents to indicate stress, as is common practice in (anglophone) Russian linguistics.
3. I am loathe to assign grammatical distinctions to informal gradations of unacceptability, so I see no incentive to distinguish these cases.

References

Bailyn, J. F. and Nevins, A. 2008. Russian genitive plurals are impostors. In A. Bachrach and A. Nevins (ed.), Inflectional Identity, pages 237-270. Oxford University Press.
Pertsova, K. 2005. How lexical conservatism can lead to paradigm gaps. UCLA Working Papers in Linguistics 11: 13-30.
Sims, A. 2015. Inflectional Defectiveness. Cambridge University Press.
Stump, G. 2010. Interactions between defectiveness and syncretism. In M. Baerman, G. G. Corbett, and D. Brown (ed.), Defective Paradigms: Missing Forms and What They Tell Us, pages 181-210. Oxford University Press.
Zaliznyak, A. A. 1977. Grammatičeskij slovar’ russkogo jazyka. Moskva.

[This is part of a series of defectivity case studies.]

The earliest discussion of defectivity within the generativist tradition can be found in an early paper by Halle (1973:7f.).

…one finds various kinds of defective paradigms in the inflection. For instance, in Russian there are about 100 verbs (all, incidentally, belonging to the so-called “second conjugation”) which lack first person singular forms of the nonpast tense. Russian grammar books frequently note that such forms as (8) “do not exist” or “are not used”, or “are avoided.”

(8)
*lažu ‘I climb’
*pobežu (or *pobeždu) ‘I conquer’
*deržu ‘I talk rudely’
*muču ‘I stir up’
*erunžu ‘I behave foolishly’

Subsequent work slightly lowers Halle’s estimate of 100 verbs. By combining evidence from Russian morphological dictionaries, Sims (2006) provides a list of 70 defective verbs, and Pertsova (2016) further refines Sims’ list to 63. But by any account, defectivity affects many more verb types than, for example, in the English verbs.

All of the defective verbs end in a dental consonant—s, z, t, or d—and belong to the second conjugation, in which verbs form infinitives in -et’ or -it’), and are defective only in the 1sg. non-past form, marked with a –u and a mutation of the stem-final dental.

Baerman (2008) provides a detailed history of the mutations of t and d. The modern mutations, to š and ž respectively, represent the expected Russian reflexes of Common Slavic *tʲ, *dʲ, respectively. Christianization, beginning at the close of the first millennium, brought about a period of substantial contact with southern Slavic speakers, and their liturgical language, Old Church Slavonic (OCS), contributed novel reflexes of *tʲ, *dʲ, namely č [tʃʲ] and žd [ʐd] . The OCS reflexes were found in, among other contexts, the 1sg. non-past—where they competed with the native mutations—and the past passive participle, where they were largely entrenched. Ultimately, č persisted in the 1sg. non-past but žd was driven out sometime in the early 20th century (ibid., 85). However, the latter persists in past passive participles (e.g., rodit’ ‘to give birth’ has the past passive participle roždënnyj).¹ The OCS affricate mutations are rarely found in contemporarily written Russian. However, Gorman & Yang (2019; henceforth G&K) cite some weak evidence that the OCS mutation has some synchronic purchase in the minds of Russian speakers. First, Sims (2006) administers a cloze task in which Russian speakers are asked to produce the 1sg. non-past of a defective verb shown in the infinitive (e.g., ubedit’ ‘to convince’) and several participants select the OCS-like ubeždu, which is proscribed. Secondly, Slioussar and Kholodilova (2013), Pertsova (2016), and Spektor (2021) catalog what happens when verbs borrowed from English end in a dental consonant. For instance, from the English friend comes zafrendit’ ‘to add s.o. to one’s friend list on social media and rasfrendit’ ‘to unfriend s.o. on social media’, and among the many options, they find instances of the OCS-like zafrenždu in addition to the expected zafrenžu. To add to the confusion, there there is some hesitation on the part of Russian speakers to apply either of the expected 1sg. non-past mutations, and some speakers produce the the unexpected, unmutated zafrendu.² There is no precedent for this among native Russian verb lexemes.

The mutations of s and z to š and ž, respectfully, have no competitor inherited from contact with OCS. These mutations occur across the board. However, that’s not quite the whole story: English borrowings in the Slioussar and Kholodilova corpus often fail to alternate. For instance, for fiksit’ ‘to fix s.t.’, they record both the expected fikšu as well as the unexpected, unmutated fiksu. 

G&K develop an account of the Russian verbal gaps which assume that each of these four dental consonants does have a synchronically active competitor, and that there is simply no default. They couch this in terms of the Yang’s Tolerance Principle, but even one rejecting that particular method of deciding what is and is not productive might still agree with the basic insight—as indicated by English dental-stem loanwords—that the dental mutations are no longer productive and that this lack of productivity, along with sparse data during acquisition, results in defectivity.

Other accounts of this phenomena can be found in ch. 7 of Sims 2015 and in Pertsova 2016. These two studies contain many interesting suggestions for future work. However, with respect I must say I am not sure how to operationalize their suggestions as part of a mechanistic account of these observations.

Postscript

The aforementioned defectivity is the subject of occasional humor among Russian speakers. For instance, as discussed by as discussed by Sims (2015:5), a Russian translation of one of Milne’s Winnie the Pooh stories has the anthropomorphic bear puzzling over the 1sg. of pobedit‘ ‘to be victorious’. This suggests that Russian verbal defectivity has risen to the level of consciousness, and may reflect sociolinguistic “change from above”.

Endnotes

1. This form was cited in G&K:186; I have taken the liberty of fixing an inconsistency in the transliteration: there рождённый was transliterated as roždënny (note the missing final glide).
2. Russian has many indeclinable nouns, nouns which do not bear the ordinary case-number suffixes (Wade 2020:§36-40). For instance, radio ‘ibid.’ and VIČ ‘HIV’ can be used in any of the six cases and two numbers, but never bears any case-number suffixes. Crucially, though, indeclinables, unlike the aforementioned verbs, are either phonotactically-odd loanwords or acronyms, but as far as I can tell there is nothing phonotactically odd about zafrendit’ or its stem. And one should certainly not equate indeclinability and defectivity.

References

Baerman, M. 2008. Historical observations on defectiveness: The first singular non-past. Russian Linguistics 32: 81-97.
Gorman,. K. and Yang, C. 2019. When nobody wins. In F. Rainer, F. Gardani, H. C. Luschützky and W. U. Dressler (ed.), Competition in Inflection and Word Formation, pages 169-193. Springer.
Halle, M. 1973. Prolegomena to a theory of word formation. Linguistic Inquiry 4: 3-16.
Pertsova. 2016. Transderivational relations and paradigm gaps in Russian verbs.
Glossa 1: 13.
Sims, A. 2006. Minding the gap: Inflectional defectiveness in a paradigmatic theory. Doctoral dissertation, Ohio State University.
Sims, A. 2015. Inflectional Defectiveness. Cambridge University Press.
Slioussar, N. and Kholodilova, M. 2011. Paradigm leveling in non-standard Russian. In
Proceedings of the 20th meeting of Formal Approaches to Slavic Linguistics, pages 243-258.
Spektor, Y. 2021. Detection and morphological analysis of novel Russian
loanwords. Master’s thesis, Graduate Center, City University of New York.
Wade, T. 2020. A Comprehensive Russian Grammar. Wiley Blackwell, 4th edition.

[This is part of a series of defectivity case studies.]

I have already written a bit about reduplication in Kinande; it too is an example of inflectional defectivity, and here I’ll focus on that fact.

In this language, most verbs participate in a form of reduplication with the semantics of roughly ‘to hurriedly V’ or ‘to repetitively V’. Mutaka & Hyman (1990; henceforth MH), argue that the reduplicant is a bisyllabic prefix. For instance, the reduplicated form of e-ri-gend-a ‘to leave’ is e-ri-gend-a-gend-a ‘to leave hurriedly’, with the reduplicant underlined. (In MH’s terms, e- is the “augment”, -ri the “prefix”, and -a is the “final vowel” morpheme.)

Certain verbal suffixes, known to Bantuists as extensions, may also be found in the reduplicant when the reduplicant would otherwise be less than bisyllabic. For instance, the passive suffix, underlyingly /-u-/, surfaces as [w] and is copied by reduplication. Thus for the verb root hum ‘beat’ the passive e-ri-hum-w-a reduplicates as e-ri-hum-w-a-hum-w-a. More interesting is there are “unproductive” (MH’s term) extensions.¹ Verbs bearing these extensions rarely have a compositional semantic relationship with their unextended form (if an unextended verb stem exists at all). For instance, whereas luh-uk-a ‘take a rest’ may be semantically related to luh-a ‘be tired’, but there is no unextended *bát-a to go with bát-uk-a ‘move’.

Interesting things happen when we try to reduplicate unproductivity extended monosyllabic verb roots. For some such verbs, the extension is not reduplicated; e.g., e-rí-bang-uk-a ‘to jump about’ has a reduplicated form e-rí-bang-a-bang-uk-a. This is the same behavior found for “productive” extensions. For others, the extension is reduplicated, producing a trisyllabic—instead of the normal bisyllabic—reduplicant; e.g., e-ri-hurut-a ‘to snore’ has a reduplicated form e-ri-hur-ut-a-hur-ut-a. Finally, there are some stems—all monosyllabic verb roots with unproductive extensions—which do not undergo reduplication; e.g., e-rí-bug-ul-a ‘to find’ does not reduplicate and neither *e-rí-bug-a-bug-ul-a or *e-rí-bug-ul-a-bug-ul-a exist.

While one could imagine there are certain semantic restrictions on reduplication, like in Chaha, MH make no mention of such restrictions in Kinande. If possible, we should rule out this as a possible explanation for the aforementioned defectivity.

Endnotes

1. I will segment these with hyphens though it may make sense to regard some unproductive extensions as part of morphologically simplex stems.

References

Mutaka, N. and Hyman, L. M. 1990. Syllables and morpheme integrity in Kinande reduplication. Phonology 7: 73-119.

[This is part of a series of defectivity case studies.]

Rose (2000) describes a circumscribed form of defectivity in Chaha, a Semitic language spoken in Ethiopia. Throughout Ethio-Semitic, many verbs have a frequentative formed using a quadriliteral verbal template. Since few verb roots are quadriconsonantal—most are triconsonantal, some are biconsonantal—a sort of reduplication and/or spreading is used to fill in the template. In Tigryina, for instance (p. 318), the frequentative template is of the form CɘCaCɘC. Then, frequentative of the triconsonantal verb root √/grf/ ‘collect’ is [gɘrarɘf], with the root /r/ repeated, and for a biconsonantal verb root like √/ħt/ ‘ask’, the frequentative is [ħatatɘt], with three root /t/s.

Rose contrasts this state of affairs with Chaha. In this language, the frequentative template CɨCɘCɘC cannot be satisfied by a biconsonantal root like √/tʼm/ ‘bend’ or √/Rd/ ‘burn’, and all such verbs lack a frequentative.¹ The expected *[tʼɨmɘmɘm] and *[nɨdɘdɘd] are ill-formed, as are all other alternatives. Furthermore, no frequentatives of any sort can be formed with quadriconsonantal roots.

Rose notes that there are often semantic reasons for a verb to lack a frequentative (e.g., stative and resultative verbs are generally not compatible with it), this does not seem applicable here.

Endnotes

1. As Rose explains: “R represents a coronal sonorant which may be realized as [n] or [r] depending on context…” (p. 317).

References

Rose, S. 2000. Multiple correspondence in reduplication. In Proceedings of the 23rd Annual Meeting of the Berkeley Linguistic Society, pages 315-326.

[This is part of a small but growing series of defectivity case studies.]

While there are some languages—like Greek or Russian—in which there are dozens or even hundreds of defective lexemes, in most cases defectivity is markedly constrained, conditioned by both morphological class or status and lexical identity. This is somewhat in conflict with models which view defectivity as essentially “absolute phonotactic ungrammaticality” (e.g., Orgun & Sprouse 1999; henceforth OS), since the generalizations about which items are or are not defective are not primarily phonotactic. A good demonstration of the morphological-lexical nature of defectivity comes from Turkish.

As first reported (to my knowledge) by Itô & Hankamer (1989; henceforth IH) Turkish has just a small number of monosyllabic stems. In verbs, one forms the “simple” (active) imperative using the bare stem: e.g., ye ‘eat!’. However, one cannot form a passive imperative of monosyllabic verbs. For instance, for EAT, we would expect *yen (with -n being the expected allomorph of the passive imperative), but this is apparently ill-formed under the appropriate interpretation, with no obvious alternative.¹ I say it this way because because yen exists as is the simple imperative ‘conquer!’. As IH note, this shows there is nothing phonotactically wrong with the ill-formed passive imperatives. Another example they give is kon ‘alight! (like a bird)’. Apparently, we would expect it to have a passive imperative homophonous with the simple imperative, but it is ill-formed under this interpretation. However, I find these two examples less than convincing since one could imagine that the homophony with another type of imperative might be implicated in these judgments.

Something similar characterizes certain monosyllabic noun stems. Turkish has apparently borrowed the seven solfège syllables do, re, mi, etc. Of these, six are CV monosyllables, which we would expect to select the /-m/ allomorph of the 1sg. poss. suffix. However, these 1sg. poss. forms are apparently ill-formed; e.g., *do-m ‘my do‘, re-m ‘my re‘, *mi-m ‘my mi‘, and so on. However, one can use these with the other declensional suffixes which produce polysyllabic outputs; e.g., 1pl. poss. domuz ‘our do’. The same facts are true for the names of the letters of the (Latin, post-1928) alphabet: e.g., de ‘the letter d’, but *de-m ‘my letter d’, and so on. OS report however that the one CVC solfège syllable, sol, has a well-formed 1sg. poss.; this selects the /-Im/ allomorph (where /I/ is a high vocalic archiphoneme subject to stem-controlled vowel harmony), which gives us the licit 1sg. poss. solüm [solʲym] ‘my sol‘.² The same facts hold of the 2sg. poss. ‘your __’, which for CV monosyllables would be realized as /-n/; e.g., *do-n ‘your do‘.

From the above facts IH and OS conclude there is an exceptionless constraint in Turkish such that monosyllabic derived forms produced by the grammar are ill-formed, with no possible “repair”. However, Selin Alkan (p.c.) draws my attention to at least one CV nominal stem which is well-formed in the 1sg. and 2sg,. poss.: su ‘water. For this stem, a [j] glide is inserted between the vowel and the stem, and the stem selects for the -VC allomorphs of the possessive; e.g., su-y-um ‘my water’, su-y-un ‘their water’. This is surprisingly insofar as OS take pains (p. 195f.) to specifically rule out repair by epenthesis in 1sg. poss. forms!

It would be nice to conclude that the only affected lexemes are transparent borrowings, but this does not seem to accord with the evidence from monosyllabic verbs. But the evidence from native stems is really quite weak, and the generalizations are clearly morphological (i.e., the restriction of the constraint to derived environments) and lexical (i.e., the fact that su has an “escape hatch”), something that has largely been ignored in previous attempts to describe defectivity in Turkish.

To move forward on this topic, it would be nice to know the following. How many, if any,  verbs behave like ye or kon, and are any unexpectedly well-formed in the passive imperative? Are there any other forms in the verbal paradigm that show “monosyllabism” gaps? Similarly, how many (if any) defective nouns are there beyond those already mentioned, and how many behave like su?

[h/t: Selin Alkan]

Endnotes

1. IH note (p. 61, fn. 1) that the passive imperative “are somewhat odd in normal circumstances”. Therefore, they asked their informants to imagine they were directors giving instructions to actors, which apparently helped to render these examples more felicitious.
2. It seems plausible that -m and -n here are purely-phonological allomorphs of /-Im, -In/ respectively, but I am not sure.

References

Itô, J. and Hankamer, J. 1989. Notes on monosyllabism in Turkish. In J. Itô and J. Runner (ed.), Phonology at Santa Cruz, pages 61-69. Linguistics Research Center, University of California, Santa Cruz.
Orgun, C. O. and Sprouse, R. L. 1999. From MPARSE to CONTROL: deriving ungrammaticality. Phonology 16:191-224.

[This is part of a small but growing series of defectivity case studies. Here I am well out of my linguistic comfort zone, working with a language I know very little about, so please take my comments cum salo granis.]

The behavior of the Tagalog actor focus (AF) infix (and occasionally, prefix) -um- has received an enormous amount of attention since the days of prosodic morphology. Schachter & Otanes (1972; henceforth SO), cited in Orgun & Sprouse (1999), claim that “-um- does not occur with bases beginning with /m/ or /w/” (p. 292). Presumably this statement means such bases are defective with respect to their actor focus form; that is certainly how Orgun & Sprouse—and most of the subsequent literature—has interpreted this. I am aware of one complication, however. First off, many verbs instead use the prefix mag– to mark actor focus; SO could simply be making a distributional statement about two allomorphs of the actor focus marker. As I understand it, whether a verb takes -um-, mag-, or both is conditioned by verb semantics, whether or not the verb is derived or a bare root, whether or not the verb is borrowed or not, and so on, and there is probably some regional, register, and individual variation too.¹ And there are other focus markers beyond -um- and mag-.

Orgun & Sprouse (henceforth OS) provide just a few examples (p. 206). According to them, there is no AF form *mumahal ‘to become expensive’ (< mahal). It’s not really clear what we ought to reason from *mumahal. First, do all adjectives have a corresponding AF verb form? Secondly, one might ask whether magmahal is the AF form of this adjective. According to Wiktionary, it is, so this is probably just an instance of ordinary morphological blocking. Third, this is obviously a loanword, which might have something to do with its choice of AF affix and/or whether it participates in the AF system at all. Similarly, OS give the example *mumura ‘to become cheap’ (< mura), but Wiktionary says magmura exists and has the relevant reading. If this is correct, OS may have confused defectivity and blocking.

OS provide two other types of examples of what they call defectivity.

First, OS claim that /Cw…/-initial stems borrowed from English can form AF forms of the form /C-um-w…/ but not /Cw-um…/. Thus the AF infinitive sumwer (< Eng. swear) well-formed, but *swumer is not. It is not clear this generalization is correct, since Ross (1996) elicits the AF infinitive [twumɪtɘɾ] (< Eng. twitter; p. 15) from “a native speaker of Tagalog in her thirties who had recently come to Canada from Manila…” who was “asked to ‘borrow’ hypothetical English loanwords…” (p. 2).² OS do not discuss /Cm-…/-initial borrowings, and they give us no reason to suspect that /Cw…/- and /Cm…/-initial loanword stems would behave differently, but Ross also elicits [smumajl] (< Eng. smile; p. 15).

Secondly, OS claim that /m, w/-initial stems borrowed from English do not form AF verbs in -um-. I have not been able to find any of their examples in a Tagalog dictionary, so these may just be poorly assimilated loanwords. 

OS note that there is no general restriction on homomorphemic /…mum…/ sequences in Tagalog, and they note that reduplication may also produce /…mum…/. Even if their description is correct, it is a mystery why this restriction holds only of a specific AF affix. But I suspect that OS have either misunderstood SO, or perhaps misgeneralized from OS’s admittedly vague comment.

Before I conclude, I should note that the empirical situation for Tagalog linguistics is dire. The language has many tens of millions of speakers, and has long been of interest to linguists. There are extensive grammatical resources on Tagalog in English and Spanish. Yet any time I interact with Tagalog examples in the literature, I find data inconsistencies, analytical laziness, or both. As a student put it to me: “As a Filipina it feels disrespectful and offensive, and as a linguist it feels super shady and raises so many philosophy of science red flags.” There may be some relevant results in Zuraw 2007, which elicits a corpus of the AF forms of Tagalog loanwords, including forms in /Sm-…/, but I am unable to reconcile those findings with Ross 1996, despite the fact that Ross and Zuraw are the same person.

Endnotes

1. For roots that take both affixes, the two AF forms may or may not be synonymous. For example, pumunta and magpunta are roughly equivalent AF forms of ‘to go’. However, bumuli means ‘to buy’ whereas magbili means ‘to sell’.
2. Note that it was the ’90s, mannnnnn, so this is about songbirds; it has nothing to do with microblogging.

References

Orgun, C. O. and Sprouse, R. L.  1999. From MPARSE to CONTROL: deriving ungrammaticality. Phonology 16:191-224.
Ross, K. 1996.  Floating phonotactics: variability in reduplication and infixation in Tagalog loanwords. Master’s thesis, University of California, Los Angeles.
Schachter, P. and Otanes, F. 1972. Tagalog Reference Grammar. University of California Press.
Zuraw, K. 2007. The role of phonetic knowledge in phonological patterning: corpus and survey evidence from Tagalog infixation. Language 83: 277-316.

[This is part of a small but growing series of defectivity case studies.]

Icelandic is not the only Scandinavian language to exhibit defectivity in imperatives: Rice (2003, 2004; henceforth R) describes a superficially similar pattern of defectivity in Norwegian adjectives.

In Norwegian, the infinitival form of most verbs consists of the particle å, the verb stem, and a schwa (which, like in German, is spelled -e). Such verbs’ imperatives then consists of the bare stem, without a particle or the schwa; e.g., å skrive ‘to write’/skriv ‘write!’. A second, smaller class of verbs are monosyllables ending in a (non-schwa) vowel. These verbs use the bare verb stem in both infinitive and imperative; e.g., å tre ‘to step’/tre ‘step!’. While R does not go into any details about how these two patterns might be encoded, one might posit two allomorphs of the infinitive suffix, -e and zero. Presumably this allomorphy is in part lexically conditioned, since it seems necessary to distinguish between minimal pairs like å vie ‘to dedicate’/vi ‘dedicate!’, which belongs to the former class, and å si ‘to say’/si ‘say!’, which belongs to the latter. However, R only gives a few examples of vowel-final monosyllable with infinitive in -e (all other verbs of this shape have zero infinitives), so it’s possible these are just exceptions and the allomorphy conditioning is mostly phonological.

A third class of verbs are those whose stem ends in a rising-sonority consonant cluster; e.g., åpne ‘to open’, sykle ‘to bike’.¹ These superficially resemble the first class of verbs (e.g., å skrive) in that they end in a schwa in the infinitive. However, Norwegian does not permit rising sonority codas, so the expected *åpn, *sykl, and so on are ill-formed.

According to R, some speakers simply use circumlocutions to avoid the imperative of such verbs, making this a standard case of defectivity. However, R mentions several other strategies used by Norwegian speakers:²

• The word-final sonorant can be made syllabic (e.g., [oːpn̩]).
• If the cluster consists of a voiceless consonant followed by a sonorant, the sonorant can be devoiced, reducing the sonority rise (e.g., [oːpn̥]).
• One can insert a schwa to break up the cluster (e.g., [oːp.pɘn]).
• One can insert a schwa after the cluster (e.g., [oːp.nɘ]).

One question that arises is whether there are any other places in the Norwegian grammar where we would expect word-final rising sonority consonant clusters to surface. As others have noted (e.g., Albright 2009), most if not all instances of inflectional defectivity are limited to specific morphological categories. For speakers who cannot generate an imperative of verbs like åpne or sykle, is this defectivity limited to this the category of imperatives, or is it found anywhere else in the language?

Endnotes

1. R gives the infinitives of this third class of verbs without the å particle. It is unclear to me whether this is intentional or just an oversight.
2. These forms are ones I have posited on the basis of R’s description, which is not as detailed as one might like.

References

Albright, A. 2009. Lexical and morphological conditioning of paradigm gaps. In C. Rice and S. Blaho (ed.), When Nothing Wins: Modeling Ungrammaticality in OT, pages 117-164. Equinox.
Rice, C. 2003. Dialectal variation in Norwegian imperatives. Nordlyd 31: 372-384.
Rice, C. 2005. Optimal gaps in optimal paradigms. Catalan Journal of Linguistics 4: 155-170.