As a result, the popperian competition among theories is biased: a theory that accounts for the k-s alternation cannot be compared to a theory considering that k-s has nothing to do with phonology: the set of things to be explained is not the same, and wildly diverges at the scale of a language, or of phonology as such. Before theories can compete, the question thus needs to be settled what a true phonological phenomenon is.

Phonologists are thus curently in the position of, say, geologists who aim to make a theory of the characteristics of stone, but are unable to distinguish stone from plastic. They thus collect samples on which they build their theory, some of which contain 10% of plastic, others 30%, still others 60% and so on. Unsurprisingly enough, competing theories built on these wildly varying sets of empirical material then significantly diverge – not because of the theorizing itself but because of the plastic.

The issue is identified at least since the early 1970s and has produced a sizeable body of literature then (evaluation metrics), but nothing could ever be concluded: there is no pre-teoretical criterion that wold allow us to decide whether a given alternation is stone or plastic. Since the early 80s, phonologists have abandoned looking into this problem, and regular sources of evidence (elicitation, phonetics, corpora / big data, typology or conceptual arguments) stand little chance to offer any advances.

Based on electro-physiological evidence from a speech production task, Sahin et al. (2009) showed that there are at least three linguistically distinct processes that can be separated in time and space in the brain: first pieces (morphemes, words) are retrieved from long term memory (lexical access), then they are concatenated (morpho-syntax), and finally they are assigned a pronunciation (phonology). The study was performed using intracranial electrophysiology, i.e. by recording local field potentials from neuron populations using electrodes implanted (for clinical evaluation) in language-related brain regions of patients with epilepsy; the patients silently pronounced words or inflected versions of non-inflected stimuli.

Sahin et al.'s (2009) results revealed that lexical access produced a significant neural response (ERP, Event-Related Potential) at ~200ms, concatenative activity provoked an ERP at ~320ms, and phonological computation induced an ERP at ~450ms. Sahin et al. thus provide an instrument that is able to detect the presence of phonological computation in language production (although this was not necessarily their goal). Whether or not the pronunciation of contentious cases such as electricity involves phonological computation may now be tested: we predict that if neural activity at around 450ms in the relevant experimental condition is absent, the production of electricity does not involve phonological computation.

We have adapted Sahin et al.'s experimental setup to non-invasive scalp-level EEG, and a pilot study shows that their results can be reproduced using this modality. We will now run a number of contentious phenomena from a variety of languges (including the English k-s alternation known as velar softening) through our protocol in order to referee their status. Particularly exotic and contentious phenomena are identified by a PhD project on so-called Crazy Rules. In all our experiments, production-based scalp-level EEG (with IRM-supported source localization) will be flanked by behavioural data based on the same protocol and stimuli (vocal key-based reaction time), as well as by a study of the anatomic underpinnings (dMRI-based diffusion of information in the brain, subject-specific variation of the white matter).