Linguisitics

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Linguisitics

• Levels of description

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Speech and language

• Language as communication
• Speech vs. text
• Speech primary
• Text is derived
• Text is not written speech
• Speech is not (usually) spoken text
• Obviously they are related

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Levels of description

• Smallest linguistic unit is the phoneme
  (speech) or (by analogy) the grapheme (text)
• Phonemes combine to form words, or more exactly,
  morphemes
• Morpheme smallest meaningful unit of language
• Words combine to form sentences (or utterances)
  according to the rules of syntax
• Form is related to meaning via semantics
• Pragmatics deals with how language use relates to
  the real world

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Phonetics

• Study of speech sounds
• Humans are the only species that have developed
  language
• No dedicated speech organs as such
• Not all sounds are speech sounds, even though
  they do convey meaning
• Speech sounds combine in arbitrary ways to form
  words

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Phonetics

• Articulatory phonetics concerned with how speech
  sounds are produced
• Acoustic phonetics concerned with physical
  properties of speech signal
• Auditory phonetics concerned with how speech
  sounds are perceived
• All are of course related

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Possible speech sounds

• Range of sounds possible in human languages
• Consonants vs vowels
• Most consonants are pulmonic egressive
• Consonant sound is determined by place and manner
  of articulation, plus voicing, and some other
  features
• Vowel sound is determined by tongue height and
  position (front/back) plus lip shape
  (round/spread)

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Phonemes

• Huge number of possible distinctions, but not all
  are significant in any given language
• Differences that are used to distinguish words
  are phonemic
• Phoneme group of (similar) sounds perceived by
  speakers as the same
• Other differences between allophones
• Phonemic distinction in one language may be
  allophonic in another
• (-etic -emic allo- -ology)

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Prosody

• Besides individual speech sounds, other features
  of speech can carry meaning
• Length, volume, pitch
• Intonation (pitch)
• Can be syntactic or lexical (in some languages)
• Stress (combination of all three)
• Lexical or semantic/pragmatic

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Writing and text

• Various writing systems worldwide
• Most familiar is alphabetic
• Ideally each letter represents a sound (phoneme)
• Rarely 11 mapping
• Phoneme can have different spellings
• Individual letter can be different phoneme
• Some phonemes represented by combination of
  letters (not always contiguous)
• Other possibilities consonantal, syllabic,
  ideological, and various combinations

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Graphemes

• Latin alphabet has 26 letters
• But English has 50 phonemes
• Phoneme can have different spellings
• /s/ can be s, c, sc, ss,
• Individual letter can be different phoneme
• c can be /s/ or /k/
• Some phonemes represented by combination of
  letters
• /?/ th, /?/ sh

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Morphology

• Smallest meaningful unit of language is the
  morpheme
• Some words are single morphemes (meaning cant be
  broken down), but many words have constituent
  parts
• Words usually consist of a root plus affix(es),
  though some words can have multiple roots
• Lexeme abstract notion of group of word forms
  that belong together
• lexeme root base form dictionary (citation)
  form

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Role of morphology

• Commonly made distinction inflectional vs
  derivational
• Inflectional morphology is grammatical
• number, tense, case, gender
• Derivational morphology concerns word building
• part-of-speech derivation
• words with related meaning

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Morphological processes

• Affixes prefix, suffix, infix, circumfix
• Umlaut, ablaut
• Gemination, (partial) reduplication
• Root and pattern
• Stress (or tone) change
• Sandhi

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Language typology

• Based on extent to which morphological processes
  play a role
• Agglutinative morphological affixes can be
  stacked up almost indefinitely
• Implies that list of possible words is infinite
• Synthetic little or no affixation
• Extent of morphology can interact with syntax
  highly inflected languages often have freer word
  order

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Morphemes

• Morphemes associated with meaning
• (Like phonemes) not 11
• Single morpheme can have various allomorphs
• Allomorphic variation usually conditioned, either
  intrinsically, or extrinsically (phonotactics,
  morphosyntax)
• Can be free variation
• Single form can represent different morphemes
• Often rules of allomorphic variation are
  systematic

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Inflectional morphology

• Grammatical in nature
• Does not carry meaning, other than grammatical
  meaning
• Highly systematic, though there may be
  irregularities and exceptions
• Simplifies lexicon, only exceptions need to be
  listed
• Unknown words may be guessable
• Language-specific and sometimes idiosyncratic
• (Mostly) helpful in parsing

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Derivational morphology

• Lexical in nature
• Can carry meaning
• Fairly systematic, and predictable up to a point
• Simplifies description of lexicon regularly
  derived words need not be listed
• Unknown words may be guessable
• But
• Apparent derivations have specialised meaning
• Some derivations missing
• Languages often have parallel derivations which
  may be translatable

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Issues for NLP

• Need scheme to handle morphology
• Can involve ambiguity which must be solved in
  analysis
• Can contribute to syntactic analysis
• Morphological analysis identifies the lexeme plus
  grammatical information associated with
  inflections
• And vice versa
• Morphological ambiguity may be resolved by
  syntactic context
• For many applications it is necessary to deal
  with just lexemes rather than word-forms and
  grammatical information stemming

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Morphological processing

• Stemming
• String-handling approaches
• Regular expressions
• Mapping onto finite-state automata
• 2-level morphology
• Mapping between surface form and lexical
  representation
• Related issues of what is in lexicon