Lecture2: Morphologystaff.um.edu.mt/mros1/csa3202/pdf/morphology.pdf · What is Morphology...

What is MorphologyMorphological Function

Morphological ProcessesMorphotactics: the order of morphemes

Orthography versus Phonology

Lecture 2: Morphology

CSA3202 Human Language Technology

Mike Rosner, Dept ICSOctober 2011

CSA3202 Human Language Technology Lecture 2: Morphology 1/ 26




Acknowledgements

Richard Sproat, Morphology and Computation, MIT Press,ISBN 0-262-19314-0 (1992)Jurafsky and Marting Ch. 5 (new edition), Ch. 8 (Old edition)





Outline

1 What is Morphology

2 Morphological Function

3 Morphological Processes

4 Morphotactics: the order of morphemes

5 Orthography versus Phonology





What is Morphology?

There are several areas of linguistics which study the structureof words.

PhonologyOrthographyMorphology

These vary according to your definition of a word

A word is a sequence of phonemes (phonology)A word is a sequence of graphemes (orthography)A word is a sequence of morphemes (morphology)

Rules govern the structures under each of these definitions.





What is a Morpheme?

Definition: smallest linguistic unit that has an independentmeaning or grammatical function

free morpheme: morphemes that can stand alone as words.e.g. clock, sickbound morpheme: morphemes that always attach to othermorphemes, never existing as words themselvese.g. -ly, non-





Words: Parts of Speech

Words are traditionally classified into categories, known asparts of speech (POS) or word classes.The major parts of speech are noun, verb, adjective, adverb,pronoun, preposition, conjunction, article etc.Subcategorization of some major POS e.g. nouns

proper nouncommon noun

Open classes and closed classesContent words vs. function words

POS can shed light on the context in which a word can occur,its neighbours and even its pronunciation

“òbject” (noun) vs “objèct” (verb)Many words are ambiguous: bankTrouble ahead for some tasks

POS taggingWordsense disambiguation





Two Different Kinds of Morphology

Morphology can be broadly divided into two different classes:

Inflectional MorphologyInput: a wordOutput: a different form of the same wordExample: wasal → waslu

Derivational MorphologyInput: a wordOutput: a different word that is derived the input word.Example: important → unimportant

issue: What is meant by a different word?





Differences between Inflectional and DerivationalMorphology

Inflectional MorphologyDoes not change part of speech.Particular inflections may be required in particular syntacticcontexts such as subject and object positions:“I like her” versus “me like she”.Productive: tends to apply across the board - especially to newwords e.g. “I was googling all day”.Predictable semantics: +s applies to most nouns and almostalways means plural.

Derivational MorphologyChanges part of speechSyntactic context never requires particular derivation.Not very productive: “dislike”, “dishate*Unoredictable semantic effect: “business” versus “happiness”.





Morphological Function

What forms?What information?The kind of information depends to some extent on the part ofspeech concerned,

VerbNounAdjective

and also to whether we are talking about derivational orinflectional morphology





Verb Forms(Inflectional)

EnglishTalkTalksTalkingTalked

Italianparlareparloparliparlaparliamoparlateparlono





Verb Information

personnumbergenderIn many languages the verb must agree with one or more of itsarguments on such information.e.g. Subject-verb agreement in FrenchLes filles sont arrivées - the girls arrived.

Example

arriv + é + e + s

arrive + past + fem + plur





Verb Information: Tense and AspectInflectional

Tense: the time at which the situations denoted by themoccurred

pastpresentfuture

Aspect: the state of completion of the action denotedThis is the distinction we observe in

I waited for three hours (perfective aspect)I am waiting for the bus (imperfective aspect)





Languages Differ

Tense and aspect are marked in different ways by differentlanguagesparleròI will speakMaltese se nkellemIn Chinese it is e.g. tashui+le = he sleep + PERFECTIVE





Verb Information: VoiceInflectional and Derivational

Voice: Active vs. PassiveActive: John brings the book downPassive: The book is brought down by John

In English active/passive is marked syntactically i.e at sentencelevel.In many other languages, it is marked morphologically i.e. atword levelMaltese example derived from niżel (to descend)

niżel (he descended) → niżżel (he brought down)niżżel (he brought down) → tniżżel (be brought down)





Nouns and Pronoun Information

Inflectional categories for nouns and pronouns includeNumber (singular, plural, dual)fortizz+a, fortizz+i, gh̄ajn+ejnCase (marks different relationships to the verb)

Nominative (subject), accusative (object), as seen inEnglish pronouns: he, himLatin nouns tabul+a, tabul+a+m

German has four cases: nominative, genitive, dative,accusative but only genitive is marked on the noun.Latin has sixFinnish has fourteen!

Gender (feminine, masculine, neuter)In some languages, such as the Bantu languages, more detailedgender classes exist.





Adjectives

Some languages express number, gender, case morphologicallyFrench: bon, bons, bonne, bonnes (good).Many languages express comparison of adjectivesmorphologically.English

Hard (unmarked - stem)Harder (comparative + er)Hardest (superlative + est)Sometimes the e is omitted.

In English comparison is sometimes expressed with syntax.“more different” not “differenter”





Derivational Morphology

Recall that derivations are category-changingTypical examples involving nouns, adjectives and verbs

Nominalization (verb → noun):destroy → destruc+tioncatch → catch+er

Deverbal adjectives (verb → adjective)The English suffix -able attaches to transitive verbs x andmeans able to be x’edExample drink → drink+able;

Nominalized adjective (noun → adjective)

The English suffix -less attaches to nouns x and meanssomething not possessing xExample brain → brain+less;





Morphological Processes

Linear Concatenation, where a morphologically complex wordcan be analyzed as a series of morphemes concatenatedtogether as with prefixes and suffixes: en + large + ment.Non-Linear Concatenation

infix

Bontoc (Philippines)fikas strong; fi+um+ikas be strongkilad red; fi+um+ikas be red

circumfix:German ge + stem + te.g. sagen, gesagtMaltese negative: ma + naf + x






Reduplication, e.g. in Indonesianorang man → orang+orang (men)Note that although reduplication is concatenative, it iscontext-dependent. What is inserted depends on what comesbefore.Vowel change

swim/swamConsonant change

send/sent






Interdigitation: a basic charateristic of Semitic languages(Maltese, Arabic, Hebrew, Akkadian, Syriac...)

Input radicals + vocalismOutput stemExample k t b + i e → kiteb

Interdigitation is an example of a non-concatenative operation.The output stem is then used as a basis for furthermorphological operationsn + kiteb + u → niktbu

Note that the end result is not nkitebu





Compounding

In contrast to derivations and inflections, where affixes areattached to a stem, in compounding two or more lexemes arejoined together.Both lexemes might undergo modification in the process.In German, the concatenation is expressed in the orthography:

Examplelebensversicherungsgesellschaftsangestellter

(life insurance company employee)leben s versicherung s gesellschaft s angestellter

life insurance company employee





Morphotactics

Morphotactics investigates the constraints imposed on theorder in which morphemes are combined.Various kinds of such constraints are known.Constraints on the type of affix

“un” is a prefix“tion” is a suffix

Syntactic constraintsthe suffix -able applies to verbs to yield an adjective

Other constraints:

in English, “Latin” affixes are attached before “native” ones:non+im+partial non+il+legiblein+non+partial in+non+legible





Why is Morphology Useful?

Almost all natural language applications require someprocessing of words.

Dictionary toolsInformation RetrievalSpellcheckingMachine Translation

When these are written, there is often a mismatch betweenwhat appears on the page, and what appears in the dictionary.The severity of this problem depends on the languageMorphological processing helps to bridge the gap.





Summary

Morphological structure conveys important information ofdifferent typesMorphological structure is manifest in different ways.Morphological structure is governed by rules.Morphological analysis attempt to discover that structure.


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