[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 SO’s admittedly vague comment.

Before I should 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.