LIN 3098 Corpus LinguisticsLecture 7

Albert Gatt

In this lecture We look at some ways in which

corpora can be useful in morphological research.

Main focus: morphological productivity

Part 1

Morphology, corpora and productivity

Productivity in linguistics The term “productivity” is used in a

wide variety of contexts. Syntactic rules are “productive” in the

sense that they can be used to generate new phrases.

The same can be said of some morphological rules.

A definition of productivity A linguistic process is productive if:

It can be used to produce novel forms.

If a rule is productive, then: Novel forms (previously unheard) can be

understood and produced; There is no need to store all forms in the

mental lexicon.

A couple of examples Imagine an English adjective garmy. How would you

derive a noun out of this adjective? Many speakers might say garminess This suggests that –ness suffixation is a productive

derivational process.

E.g. Imagine a Maltese verb intoffa. How would you produce a noun from it? Speakers might say intoffar or inttofament or

intoffazzjoni This suggests that –ar and –ment suffixation are

productive derivational processes in Maltese.

Productive vs non-productive Some morphological processes or

categories seem to have greater potential to form new words than others e.g. English -able, -ness compare to English –th: warmth,

strength… (much less productive)

Classical approaches to productivity Jackendoff (1975):

morphological rules are called redundancy rules: They capture the relationship between related forms

E.g. Warm warmth (ADJ N via addition of –th) E.g. Desire desirable (N ADJ via addition of –able)

If a rule is productive, then it can be used to create novel forms. e.g. adjectives with –able can be produced

“online”

Features of classical approaches1. Relies on a binary distinction

(un/productive)

2. Productive rules are typically regular & sub-regularities not considered much (Dressler 2003)

3. Most of these approaches do not look at corpus data

Productive vs regular Usually, productive morphological rules are regular.

Irregular forms are likely to be stored in the lexicon.

However, we can sometimes detect “sub-regularities”: sing-sang ring-rang bring-brang (?)

Speakers can sometimes generalise these sub-regular processes, perhaps by analogy. What’s the past tense of tring or spling?

“Possible” vs “attested” Our tentative definition of productivity focuses on

production of novel forms.

By definition, novel forms are: Possible words of the language; Previously unattested.

This would suggest that we can’t use corpora to study productivity. Corpora only contain attested forms.

The problem of frequency Suppose we find that a corpus contains lots of words

ending in some suffix –X.

This doesn’t necessarily imply that the -X suffix is productive.

It could have been productive in the past, but is not anymore. Therefore, the likelihood of a new word ending in –X

is low, despite the high frequency.

Getting around the problem Frequency can’t give us all the answers. However, one

interesting solution is to look at hapax legomena.

A corpus will usually contain lots of words occurring only once.

We can think of hapaxes as “one-offs”.

It seems likely that some hapaxes will be “new formations” NB We can only make this assumption if the corpus is very large.

Corpus-based approaches View productivity as a gradable

phenomenon: some forms become ingrained through frequent

usage category can still be productive to some extent productivity estimated in terms of a category’s

potential to produce new forms can account for sub-regularities: productivity of a

category is due to a lot of factors, including analogy to existing words

The continuum

Productive processes tend to: be compositional result in a lot of new words

Productive morphological process

lexicalised word

ADJ+ness Noun ADJ+th Noun

Why is productivity interesting? No finite lexicon can contain all words of a

language at a certain time productive processes can be exploited to parse

new/unseen lexical items this is helped by the compositionality of

productive processes can also help to distinguish creative neologism

from systematic rule-application. compare: well-defined, well-intentioned, well-specified

lots of adjectives with a well- prefix YouTube

a one-off

Theoretical implications raises interesting questions about the

relationship between corpus-based measures and psycholinguistic data

likelihood of a morphological process being applied depends on style, genre, speech community…

can give an indication of language change over time (some processes are fossilised, others become more productive)

Statistical measures of productivity (Baayen 2006)

What we need A measure of productivity of a

process/category C should reflect: our intuitions about how frequently we

encounter C how easily native speakers can form new

words using C Is it easier to produce a noun with –th

(like warmth) or one with –ness (like goodness)?

An analogy We can compare morphological processes to companies.

All try to dominate a market where the number of clients (words) is limited.

Productivity reflects the extent to which these companies: have managed to dominate in the past (how many

words they’ve formed) are expanding into new areas of the market (how

many new words they’re forming) may expand in the future (how many as yet unseen

words they’re going to form)

Realised productivity (RP) Given a morphological category C, RP

gives a rough indication of the past utility of C in forming new words.

Measured as the number of distinct types in C in a corpus of size N

E.g. regular past tense –ed displays many more types than sub-regular forms such as keep-kept/sleep-slept

Realised productivity cont/d Why types, not tokens?

Productive processes have lots of types which are hapaxes, or are very infrequent (low token frequency).

Words formed from irregular processes tend to be very frequent (have high token frequency).

Some limitations: a high RP for a category does not imply that it

will keep forming lots of new words RP is heavily dependent on corpus size

Expanding productivity (P*) P* gives a rough indication of the rate of

expansion of C. Focuses on the number of hapaxes

produced using C in the corpus. aka hapax-conditioned productivity

NB: P* is still heavily dependent on corpus size!

corpusin hapaxes of no. totalC using formed hapaxes of .* NoP

Potential productivity (P) Gives an indication of how likely a category

C is to form new words in future. I.e. the potential for C to be already saturated aka category-conditioned productivity

C using formed tokensof no. totalC using formed hapaxes of No.* P

Some more on P Unlike RP and P*, P is not very sensitive to

corpus size as such However, very sensitive to frequency of the

category. e.g. if C is realised only once in a corpus of size

N, then P = 1! Recent empirical work has shown that RP

and P* may correlate very strongly, but both exhibit a weak correlation with P (Vegnaduzzo 2009) pattern non-X has high RP and P*, but low P pattern X-ish has low RP and P*, but high P

P vs. RP and P* A category C can have low RP and P*,

but high P. In this case, C hasn’t been used much in the

past, but is being used quite productively at the moment.

Corresponds to the “ease” with which new words can be formed using the category.

If category has high RP, it may still be saturated, so have low P.

The psycholinguistic connection1. Rule vs. direct access:

To produce a word (e.g. illegal), you can either store it directly, or apply the rule on the fly.

Evidence suggests that frequency of baseform vs. derivation is related to which of the two alternatives apply.

The psycholinguistic connection2. Complexity-based affix ordering:

Corpus research: more productive affixes follow less productive ones in word formation

It seems that more highly predictable (low productivity) affixes are processed first.

High productivity may also imply less likelihood of entering into further derivational processes.

Works cited S. Vegnaduzzo (2009). Morphological

productivity rankings of complex adjectives. Proc. NAACL-HLT Workshop on Computational Approaches to Linguistic Creativity.

K. Molinen and S. Pulman (2008). The good, the bad and the unknown: Morphosyllabic sentiment tagging of unseen words. Proc. ACL 2008

Baayen 2006 linked from web page