Phonological constraints can, in principle, be classified according to whether they are natural (founded in principles of Universal Grammar (UG)) or unnatural (arbitrary, learned inductively from the language data). Recent work has used this distinction as the basis for arguments about the role of UG in learning. Some languages have phonological patterns that arguably reflect unnatural constraints. With experimental testing, one can assess whether such patterns are actually learned by native speakers. Becker, Ketrez, and Nevins (2007), testing speakers of Turkish, suggest that they do indeed go unlearned. They interpret this result with a strong UG position: humans are unable to learn data patterns not backed by UG principles. This article pursues the same research line, locating similarly unnatural data patterns in the vowel harmony system of Hungarian, such as the tendency (among certain stem types) for a final bilabial stop to favor front harmony. Our own test leads to the opposite conclusion to Becker et al.: Hungarians evidently do learn the unnatural patterns. To conclude we consider a bias account—that speakers are able to learn unnatural environments, but devalue them relative to natural ones. We outline a method for testing the strength of constraints as learned by speakers against the strength of the corresponding patterns in the lexicon, and show that it offers tentative support for the hypothesis that unnatural constraints are disfavored by language learners.

Using a combination of magnetometry and ultrasound, we examined the articulatory characteristics of the so-called ‘transparent ’ vowels [i�], [i], and [e�] in Hungarian vowel harmony. Phonologically, transparent vowels are front, but they can be followed by either front or back suffixes. However, a finer look reveals an underlying phonetic coherence in two respects. First, transparent vowels in back harmony contexts show a less advanced (more retracted) tongue body posture than phonemically identical vowels in front harmony contexts: e.g. [i] in buli-val is less advanced than [i] in bili-vel. Second, transparent vowels in monosyllabic stems selecting back suffixes are also less advanced than phonemically identical vowels in stems selecting front suffixes: e.g. [i�] in ír, taking back suffixes, compared to [i�] of hír, taking front suffixes, is less advanced when these stems are produced in bare form (no suffixes). We thus argue that the phonetic degree of tongue body horizontal position correlates with the phonological alternation in suffixes. A hypothesis that emerges from this work is that a plausible phonetic basis for transparency can be found in quantal characteristics of the relation between articulation and acoustics of transparent vowels. More broadly, the proposal is that the phonology of transparent vowels is better understood when their phonological patterning is studied together with their articulatory and acoustic characteristics.