Kisseberth’s (1970) theory of exceptionality is arguably one of the most expressive yet proposed. Roughly, Kisseberth proposes that for every rule R, every morpheme bears two equipollent features, one indicating whether the morpheme is a potential target (±R Target) and another indicating whether the morpheme is a potential trigger (±R Trigger). R then applies if and only if its structural description is met, when the target morpheme is +R target, and the trigger morpheme is +R Trigger.¹

I conjecture that Inkelas and colleagues’ notion of inalterability as prespecification, as implemented in Logical Phonology (LP), completely eliminates the need for morphemic ±R Target. Rather, particular morphemes’ ability to undergo R can be encoded via underespecification of individual target segments in those morphemes, rendering the segments mutable to feature-filling processes in contrast to fully-specified inalterable segments.² There are at least a few cases—e.g., Turkish ternary voice alternations (Inkelas & Orgun 1995) and k-deletion (Gorman & Reiss in press a), Polish yer deletion (Rubach 2013)—where it seems that target exceptionality cannot be expressed as a morpheme-level property, so we have good reason to prefer the “exceptional segments” of IAP/LP to “exceptional morphemes” with respect to targeting.³

LP generalizes the IAP notion from targets to triggers, using underspecification to render possible triggers quiescent in contrast to fully-specified catalytic segments (see, e.g., Gorman & Reiss in press b). However, I conjecture that a complete theory will still need rules which are triggered in the context of specific morphemes or morphosyntactic contexts.

For example, consider umlaut in Standard German. Umlaut targeting is implemented by leaving o and u (which mutate to ö [ø] and ü [y], respectively) underspecified for Back; some additional complexities are raised by umlauting au and a (which mutate to äu [ɔʏ] and ä [ɛ], respectively). The primary umlaut rule is thus a unification rule which specifies these segments as -Back; separate rules fill in additional details for au and a.

Umlaut triggering is more complex. The triggers are particular suffixes: noun plurals in -er (e.g., Würmer ‘worms’), -e (Nüsse ‘nuts’), and zero (Mütter ‘mothers’), the diminutive -chen (Häuschen ‘little house’), comparatives and superlatives of adjectives (größerer ‘bigger’, am größten ‘biggest’), and 2nd/3rd singular present indicative (du fängst ‘you catch’, er fängt ‘s/he catches’), and a few others.  These suffixes have nothing in common morphosyntactically, and exclude related suffixes like noun plural -(e)n or diminutive -lein. And crucially, the triggering suffixes have no common segments on the surface. It is true that many of these suffixes once contained an *i, but many others never did, and Janda (1998) argues umlaut triggering had a morphemic characteristic in even the earliest written German. LP could of course posit these suffixes contain /i/-triggers which never surface—such a grammar is computable, and Bach & King (1970) try to make a proposal of this form work—but Gorman & Reiss (2025) suggest that such analyses are not considered by the language acquisition device (LAD).⁴  Thus we must admit the possibility that umlaut is triggered by specific morphemes, in line with Kisseberth’s ±R Trigger.

A counterexample to the first conjecture would involve some case where targeting must be a morphemic property—what such an example would look like, I don’t know—and a counterexample to the second conjecture would involve an argument that all apparent morphemic triggering is in fact computed within the narrow phonology.

Endnotes

1.  One might imagine that some of these specifications are filled in by redundancy rules. For example, if R is productive (however that’s encoded…), maybe +R target and +R trigger are defaults but the opposite is true if a morpheme lacks the phonological or morphosyntactic properties needed to target and/or trigger R respectively. But Kisseberth doesn’t discuss this matter.
2. In contrast, when R is a segment deletion rule, a segment targeted by R is fully-specified for reasons we discuss in Gorman & Reiss in press a.
3. Of course, LP also assumes that children are epistemically bound to provide a narrow phonological analysis (like the IAP pattern), so this does not require further motivation.
4. Gorman & Reiss (2025) specifically propose a LAD principle no wandering targets; to rule out the /i/-deletion analysis, one would want to generalize that principle from targets to triggers. I see no obstacles to doing so.

References

Bach, E. and King, R. D. 1970. Umlaut in Modern German. Glossa 4:3-21.
Gorman, K. and Reiss, C. 2025. How not to acquire exchange rules in Logical Phonology. In Proceedings of the 2025 annual conference of the Canadian Linguistic Association.
Gorman, K. and Reiss, C. In press a. Natural class reasoning in segment deletion rules. Paper presented at the 56th annual meeting of the North East Linguistic Society, to appear in the proceeedings.
Gorman, K. and Reiss, C. In press b. Metaphony in Substance-Free Logical Phonology. Phonology to appear.
Inkelas, S. and Orgun, C. O. 1995. Level ordering and economy in the lexical phonology of Turkish. Language 71: 763-793.
Janda, R. D. 1998. German umlaut: Morpholexical all the way down from OHG to NHG (Two Stützepunkte for Romance metaphony). Rivista di Linguistica 10: 1563-232.
Kisseberth, C. W. 1970. The treatment of exceptions. Papers in Linguistics 2: 44-58.
Rubach, J. 2013. Exceptional segments in Polish. Natural Language & Linguistic Theory 31: 1139-1163.