Dual mechanism approaches

Pinker (1999) characterizes English past tense morphology as a prime example to understand two distinct mechanisms that lie at the basis of the human language faculty:

The premise of this book is that there are two tricks, words and rules. They work by different principles, are learned and used in different ways, and may even reside in different parts of the brain (Pinker 1999: 2).

Therefore, every human being is endowed with a set of linguistic rules and a lexicon (Pinker and Prince 1988; Prasada and Pinker 1993; Pinker 1998; Pinker and Ullman

2002). Pinker’s ideas on language and about the actual origin of those rules can be defined as innatist, as he claims that:

Inside everyone’s head there is a finite algorithm with the ability to generate an infinite number of potential sentences, each corresponding to a distinct thought. The meaning of a sentence is computed from the meanings of the individual words and the way they are arranged (Pinker 1998: 3).

Pinker (1998: 223) focuses on RVs and IVs as a means to show that words and rules are the "ingredients" of language. These forms are considered to be the ideal testing ground for a number of reasons. Both types are equated for length and complexity (being single words), for grammatical properties (being nonfinite forms, with identical syntactic privileges), and meaning (both expressing the pastness of an event or state)”.

He affirms that regulars and irregulars are processed by different mechanisms: regulars are formed by rules, while irregulars are stored in the mental lexicon. So, a combination of the main features of the previous two theories are proposed:

 Generative grammar - productive rules

 Connectionist - an associative storage facility In the same vein, Pinker and Ullman (2002) claim:

The regular–irregular distinction is an epiphenomenon of the design of the human language faculty, in particular, the distinction between lexicon and grammar made in most traditional theories of language (Pinker and Ullman 2002: 456).

They define the lexicon as a subdivision of memory that includes all arbitrary pairs of sound and meaning that refer to the morphemes and simple words of a language, while the grammar is a productive system that assembles morphemes and simple words into complex words, phrases and sentences. They also claim IVs, like other words, are acquired and stored, but with a grammatical feature like [PAST] merged into their lexical entries. RVs, by contrast, can be productive, so they can be generated by a rule, just like phrases and sentences. A stored inflected form of an irregular verb may block the application of the rule to that verb. When there is no stored irregular inflected form

for a particular stem, the default affix of a regular form is attached to that stem; so this default affix applies for any unsorted item as in the following figure:

Figure 8: Simplified illustration of the Words-and-Rules theory (based on Pinker and Ullman 2002: 457)

Hence, when a word is inflected, it (in parallel) accesses the lexicon and the grammar. If an inflected form of a verb is found in the mental lexicon (as with irregulars e.g., held), it will be successfully retrieved. Due to this match, the operation of the grammatical suffixation process is blocked preventing the generation of a form like holded. If no inflected form is matched, then the grammatical processor searches for the suitable affix to be attached to the stem and generates a regular form. In this case, thus, the default rule is applied e.g., walk-walked.

For a better understanding of the implications of this theory, we need to know what is meant by the process of morphological blocking. This process is based on the generative dogma that it is impossible to have two forms expressing the exact same idea within an individual’s linguistic repertoire at a given point in time. Don et al.

(1994) claim that this view refers to the phenomenon where the occurrence of one word blocks the possibility of generating another word with the identical meaning e.g., ran-runned.

Pinker (1984) outlines this concept as the ‘unique entry principle’. This principle refers to “the constraint that no cell in a paradigm may be filled with more than one affix” (Pinker 1984: 177). Hence, when an irregular past tense is stored in the lexicon, it prevents the rule from applying:

If a word can provide its own past tense from memory, the regular rule is blocked: that is why adults, who know broke, do not say breaked. Elsewhere (by default), the rule applies: that is why children can generate ricked and adults can generate moshed, even if they have never had a prior opportunity to memorize either one (Pinker 1998: 223).

Accordingly, whenever there is the possibility of a successful retrieval of an irregular form e.g., slept, this is said to result in the sending of a constant signal to the rule-system, which in turn blocks the application of the default rule and therefore prevents the occurrence of RFs e.g., sleeped. Nevertheless, if a memorized form cannot be retrieved because of various factors (e.g., no memory entry of irregulars as in the case of nonce-forms (e.g., ploamph) or the weakness of the memory traces of irregulars as in the case of newly acquired or very low frequency forms), the regular rule applies.

The regularization form e.g., sleeped instead of slept is called a “blocking-and-retrieval-failure” (Marcus et al. 1992; Marcus et al. 1995).

Focusing on verbs’ sensitivity to frequency, let’s compare between RVs and IVs. As RVs are produced by means of a rule, regular inflection is supposedly frequency insensitive. Pinker (1999) emphasizes this hypothesis stating that a regular form turns to have a high type frequency. The regular past tense inflection of -ed applies to 86%

of the 1000 most common verbs (Pinker 1999). Another evidence for the regulars’

insensitivity to frequency comes from plurality in German. The plural marker -s (as in Kinos (cinema.PL)) only applies to a small number of words. There are other more common plural markers e.g., e (as in Stifte (pen.PL)), er (as in Bilder (picture.PL)), -n (as i-n Vase-n (vase.PL)). No-netheless, Clahse-n (1999) a-nd Marcus et al. 1995 prese-nt experimental evidence that even in this case of ‘minority inflection’, the plural marker -s is still considered as the default marking. It is generalized to novel and derived words where no stored irregular form is available in the mental lexicon (e.g. plural Kachs rather than Käche or Kacher).

However, the situation is different with IVs that are memorized as lexical items in the mental lexicon. Thus, irregular inflection should be sensitive of frequency. In order to store IVs as wholes in memory, these forms should be frequent enough in language use to warrant such storage. Hence, in the process of learning, there is a certain threshold for complex forms to be stored in memory. If the frequency of the certain irregular form is above this threshold, then this form will be stored in the lexicon. If not, for whatever reason, the irregular form will regularize, as the default rule will be used. This is because the use of the default rule takes some effort every time it supposes to be produced. This effort is lesser in case the form can be retrieved from memory on the whole. In this regard, Pinker (1999) exposes two predictions: first, high frequent irregulars are retrieved faster than low frequency irregulars. Hence, low frequency irregulars are regularized more often than high frequency irregulars. Only words with high frequency can remain irregular without being subsumed by the regular rule. Thus, irregulars tend to have high frequency, and high frequency verbs tend to be irregular.

Second, no significant difference in retrieval rates between high and low frequency RVs. There are some empirical findings that support these predictions. The top ten frequent verbs in English, be, have, do, go, say, can, will, see, take and get, are all irregular (Pinker 1999; Lieberman et al. 2007). Similarly, KuCera and Francis (1967) exhibit that the most frequent verbs of English are all irregular, while verbs with lower frequencies are all regular. They claim that of the top 30 most frequent English verbs in the past form 22 are irregular. Additional empirical evidence originates in diachronic change: IVs that in the course of history for whatever reason become less frequent get regular inflection, several examples such as to chide, to glide and to gripe have become regular during the course of history (Pinker 1999: 69).

More findings from various empirical studies of the morphological acquisition with/against single-dual mechanism approaches will be produced in the next subsection. The main focus will be on studies of (ir)regularization processes that is particularly relevant to work in this thesis.