How do indeterminacy and ambiguity differ?

Structural ambiguities

Lecturer: Martin Volk

The content and examples of this lecture are mainly based on [Agricola 68]. Information on ambiguities in English was taken from [Hirst 87]. The main aim of the lecture, however, is to provide an overview of the various types of structural ambiguities in German. The terms ambiguity (short: MD) and Ambiguity are used synonymously.



Definition of ambiguity according to [Bussmann 83] (excerpts):

Property of expressions of natural language to which several interpretations can be assigned, or which have to be specified several times in the linguistic description under lexical, semantic, syntactic and other aspects.


Ambiguity - vagueness (pragmatic indeterminacy)
Ambiguous expressions have competing interpretations, while vague expressions have coexisting contradicting specifications. Peter is an adult.

can be biologically true and socially false at the same time.

semantic ambiguity - syntactic ambiguity
There are sentences that are semantically ambiguous, even though they are syntactically unambiguous. (Examples from S. Mehl)
  • semantic function (deep case) is ambiguous The insults of this writer are unbearable.
  • The co-reference is ambiguous The farmer's wife sold the cow because she was old and sick.
  • The scope of quantifiers and negations is ambiguous (depending on the grammar, syntactic ambiguity is also possible here) It does not own a penny.
lexical ambiguity (also: polysemy, homonymy) - syntactic or structural ambiguity (also: polysyntacticity, constructional homonymy)
Petra bought the castle. The pond beat softly shallow waves.

Agricola examines ambiguities against the background of the dependency grammar. He defines `syntactically ambiguous' (p. 62 ff., Wording changed here):

  1. One word form can be subordinated to a second more than a direct dependency relation can be attributed. This MD happens on the basis of
    • ambiguous criteria of the linear sequence (word form sequence-MD) and / or
    • of ambiguous formal syntactic components (word form MD).
    Each of these relations is either of the same type of dependency (SM I) or of a different type of dependency (SM III).
  2. One word form can be used when subordinating to a second only one direct dependency relation, but this one with more than one dependency type, can be attributed to (SM II). This MD happens on the basis of
    • multiple syntactic meanings of one and the same dependency relationship (with clear criteria of the word sequence and the word forms) or
    • Word form MD alone or combined with word form sequence MD or
    • Word form sequence MD combined with multiple dependency.

I.e. there are basically two reasons for syntactic ambiguity:

  1. Syntactically ambiguous word forms or constituents (Agricola found in a count that 70% to 80% of all word forms in a German text are syntactically ambiguous.) He reads the book to his sister.
  2. inherently ambiguous structuresOld men and women lagged behind.


Example for type SM I, two possible dependency relations with the same dependency type (PP with reference to immediately preceding or further preceding noun):

The quantization of language with a small number of levels ...

Example for SM II, a dependency relation with two different dependency types (NP as direct object or adverbial):

So he lost the whole evening.

Example for SM III, two dependency relations with two different dependency types (adjective as attribute or predicate part):

You don't know how good Calvados tastes.

Levels of structural ambiguity

Agricola distinguishes (p. 69 ff): As a result of the syntactic analysis

  1. syntactically unambiguous sentences,
  2. totally ambiguous sentences that can be locally disambiguated by non-syntactic information,
  3. totally ambiguous sentences that can be disambiguated by non-syntactic information of the wider context,
  4. absolutely ambiguous sentences.

This division is further subdivided with regard to the behavior during the analysis:

1. Syntactically unambiguous sentences

  1. Yuri Gagarin is the hero of the day.
  2. Syntactically partially ambiguous sentences

    The course of the analysis is delayed by ambiguity, but leads to the solution of the ambiguity after verification (triggered by clear parts of the sentence).

    This big chimpanzee (DO / IO) should be fed more. These big chimpanzees (DO / IO) should be given more food.
  3. Syntax temporarily ambiguous sentences

    The course of the analysis is misled by ambiguity. A complete sentence is found before the end of the input.

    For the first time, the Association of North German Surgeons chose Hamburg (DO / NP) as the conference location% Berlin (DO). And the clarity of her face was made even clearer by% her shimmering teeth%.

2. Totally ambiguous sentences with local disambiguation

After analyzing through non-syntactic meanings of the analyzed sentence

  1. Solvable ambiguities 24 dead (SN / DO) have caused floods (DO / SN) that recently ...
  2. Ambiguities of the thermal spring, which arises in one of the most beautiful forest areas of our district on earth (NG / IO), can be resolved with reservations.
  3. ambiguities that cannot be resolved, but which do not significantly impair the communicative effect.Homonyms (SN / NA) and polysemous words are treated as follows: ...

3. Totally ambiguous sentences with contextual disambiguation

After analyzing through non-syntactic meanings

  1. of the verbal context (preceding or following) solvable ambiguity The post was followed by the railway, which excluded around 1000 borrowings from (NF / FO) the German.

    (Is it the exclusion of foreign language words from German or the exclusion of German words from another language?)

  2. of the non-verbal context solvable ambiguity you better have (AB / AA) pour boiled water into the cooler.

4. Absolutely ambiguous sentences

  1. unintentional ambiguity ... to the palace that had long (NA / AB) tapestries from Angers.
  2. Intentional ambiguity You were lacking for (FO / AB) happiness. A patient young husband of Ayre Heard below his wife's piteous prayer; 'Slip on something, quick And come down, I feel sick.' So he slipped on - the very first stair.

Classification and collection of examples

The following classification is taken from [Agricola 68] (p. 89 ff). Agricola distinguishes 91 classes of ambiguity. The numbering of the original was retained. Missing numbers are either classes that only apply to English or that seemed less important and illustrative to me. Agricola arranged the classes based on the complexity of the ambiguity.

  • Classes (1) to (26) are SM I.
  • Classes (27) to (47) are SM II.
  • Classes (48) to (91) are SM III.

(1) PP attributes in a NP

(N PP PP) vs (N PP (P NP (N PP))) courses for association members abroad

(2) PP and genitive attribute in a NP

(N NP_Genitiv PP) vs (N NP_Genitiv (Det N PP)) ... manifestations of superstition in our habits Price regulation for services of the council of the district of Leipzig

(4) Genitive attribute and NP apposition in a NP

(N NP_Genitiv NP_App) vs (N NP_Genitiv (Det N NP_App)) At the invitation of a colleague of my husband, Dr. Stefan Bindler, we visited ...

(5) Genitive attribute and participle apposition in a NP

(N NP_Genitiv Part_App) vs (N NP_Genitiv (Det N Part_App)) The orbit of the new comet, first determined in 1825, ...

(6) Attribute to or in a coordinated NP

(NP (NP Koord NP) PP) vs (NP (NP Koord NP (N PP))) The author, formerly a teacher and now a student at the Literature Institute ...

Analogous for other attribute types:

The reign of terror and the happiness of Anette Martin ... ... found Ralf and the poodle, trembling with fear ...

(11) Adjective attributes in a NP

(NP (Adj Adj N)) vs (NP (Adj NP (Adj N))) ambitious young artists

(12) Adverbs in an AdjP

(AdjP (Adv (AdjP Adv Adj))) vs (AdjP (AdvP (Adv Adv) Adj)) a potentially syntactically ambiguous class

(15) Adverbs in a coordinated AdjP

(AdjP (Adv AdjP (AdjP Koord AdjP))) vs (AdjP (AdjP (Adv Adj) Koord AdjP)) She is not tall and red-haired.

(16) Verbs in a coordinated VP

(VP (V (V Coord V) NP)) vs (VP ​​(VP (V) Coord VP (V NP))) Maresia read and wrote some letters.

Analogously for other supplementary and adjunct types:

... aimed and shot at some partridges. He understood and acted immediately.

(20) Complex verb groups in a coordinated VP

(VP (V (V Coord V) ModalV)) vs (VP ​​(VP (V) Coord VP (V ModalV))) The operated patient will be able to live and work.

(21) Following or preceding genitive attribute

(NP (Det N NP_Genitiv) NP (N)) vs (NP (Det N) NP (NP_Genitiv N)) ... whereby Bühler's 'expression function' is misinterpreted by mistake. Gates sees Microsoft's most fundamental practices undermined by the government proposal. (CZ May 4, 2000)

(22) Participle apposition with ambiguous reference

(NP1 NP2 VG Part_App (to NP1)) vs (NP1 NP2 VG Part_App (to NP2)) ... when Monika met him, trembling with cold and wet.

(23) PP as an adverbial or adjective attribute

(PP (P N) NP (Part N)) vs (NP (AdjP (PP (P N) Part)) N) ... a peasant woman who regains the wisdom buried in her studies.

(24) Relative clause as an attribute to complex NP

(N PP (P NP (Det N RelS))) vs (N1 PP RelS (to N1)) ... is one of the new buildings in town that I love so much.

(25) Several relative clauses as an attribute to a NP

the change that a peasant woman is capable of, regaining her buried wisdom.

(26) Adjective attribute to or in coordinated NP

(NP (NP (Adj N) Koord NP (N))) vs (NP (Adj NP (N Koord N)))) Old men and women were affected.

This is followed by ambiguities (27-32), which (in my opinion) are doubtful as to whether they are syntactic ambiguities, since only one phrase structure is assigned to the various readings.

a cooling solution (transitive reading :) a solution that cools down a bit (intransitive reading :) a solution that cools itself down Steinberg's insult Active reading: Steinberg has insulted someone. Passive reading: Steinberg was insulted by somebody.

(33) Anaphoric vs. impersonal use of it

Forge the iron while it's warm. The sheep is sick, there is no more milk.

(34) PP as an adjunct or object.

I want to look around the libraries after my dissertation. In time we will finish.

(39) NP as adjunct or object

... she dreamed the whole trip. Every third hour there is a break.

(42) NP as subject or direct object

Ms. U. could not convince the judge that ... Yesterday the hippopotamus ate the crocodile.

(43) NP as a direct or indirect object

He preferred Frau Greiner to Frau Gärtner.

(44) NP as subject or direct object in subordinate sentence

the woman who loved Napoleon ...

(47) Adjective or adverb

They reluctantly named the perpetrator. This news is sure to be true.

(53) Adverb as an adverbial determination or attribute

... but sometimes use pictorial expressions. They stubbornly defend money that has been fraudulent.

(54) Adverb as adv. Determination or trailing attribute

As my days are numbered here ...

(55) PP as an attribute or object (agent of a passive construction)

Only with the prepositions by and of.

When the murderer was captured by Dessau ...

(56) Comparative adverb group as an attribute or adverbial

He wants to end his career as a school principal.

(57) PP as an attribute or object

After ordering, magazines are distributed at the desk in the reading room.

(61) PP as an adverbial or as an attribute to an adjective

He bought potatoes that were unusable for human consumption.

(63) NP as apposition or enumeration

She was accompanied by her sister, Princess Radzivill, officials and friends.

(65) N as an attribute or predicative

... that this barrel of beer is for the masons. ... were the last deliveries of briquettes from aspen grove.

(72) Adv / Adj as a progressive adverb or as an attribute

He knew more handicapped people.

(80) Coordination in a PP

The following applies to main clauses with inversion and subordinate clauses ... With the permission of the district council and the trade union ...

(83) NP as a genitive attribute or dative object

... to notify the dean of the faculty in writing about the cancellation of lectures.

(85) Subst / Adj in a coordination

Engaged and married couples are cared for ...

(87) Participle as a verb or as an attribute in a coordination

Today I sealed a package and sent it by registered mail.

(88) Adv / Adj as an attribute or adverbial

The freighter is putting out oil pipes.

Areas of impact of ambiguity

Agricola distinguishes between the following areas of impact:

  • the variants are structures of one and the same phrase (see example 1)
  • the variants are structures of different phrases of the same clause (see example 22)
  • one variant is the structure of a phrase, the other is the structure of the clause, both in the same clause (see example 65)
  • the variants are structures of one and the same clause (see example 33)
  • one variant is the structure of a phrase, the other is the structure of another phrase, both in different clauses (only used for English)
  • one variant is the structure of a phrase, the other is the structure of a clause, both in different clauses (see example 34)
  • the variants are clauses that depend on the same clause (see example 24, 44)
  • the variants are clauses dependent on different clauses (see example 25)

Ambiguity in German and English

The ambiguity classes are language specific. For each type, Agricola indicates whether it also appears in English. He also introduces types of ambiguity that occur in English but not in German. An example for each:

For German only (does not appear in English)
see example (83)
For German and English
See Ex. (72) He had known more attractive women ...
For English only (does not appear in German)
(73) preposition or particle He looked over the old fence.

Agricola also examined whether the type of ambiguity can be transferred from one language to the other. That is mostly the case. Exception e.g. type (47), which occurs for German and English, but so depends on specific lexical material that it is not transferable.

The new train appeared faster.

General observations

  • MDs classes can overlap. I.e. a word class sequence can be the basis for different types of MD.
  • In addition to the MD classes (a type that occurs relatively frequently in texts and apply to a relatively large number of lexical collocations), there are also ambiguous individual cases (word class sequences that are ambiguous only in very few lexical realizations and under very special conditions). E.g. forms of become ambiguous when followed by a verb form in which the past participle and infinitive match (e.g. to forget) and which is to be used both intransitive and transitive. Time flies and the child is forgotten.
  • If there are omissions, many more MDs are created. This is used in a targeted manner when formulating headlines in newspapers. Flies are not just a nuisance, but also a danger.
  • In addition to the MDs listed, there are MDs in the anaphernary resolution. Sparks set the roof of the house on fire and completely destroyed it.

Reasons for ambiguity

Agricola distinguishes 8 occasions for MDen (with 4 simple and 4 combined events):

  1. flexivically ambiguous word forms
  2. word forms ambiguous according to word class
  3. Word form sequence MDs ("The word form in question can be correctly subordinated to more than one other form in the given sequence of word class elements without violating any interval conditions.")
  4. Multiple dependencies ("In the subordinate element, two or more syntactic meanings are based on a form without the word class MD or MD in the paradigm of inflected forms." See example 55: PP as an attribute or object (agent of a passive construction))
  5. Word form sequence MDs of flexivically ambiguous word forms
  6. Word form sequence MDs of word forms that are ambiguous according to word class
  7. Word form sequence MDs of flexivically and word forms ambiguous according to word class
  8. Multiple dependencies together with word form sequence MDs

The reasons are related to the classes in the form of a table (p. 149).

An alternative classification

Another classification for structural MDs is proposed in [Hirst 87] (p. 131 ff). It is aimed at English and will only be briefly outlined here.

Attachment Problems
occur when there is more than one node to which a constituent can be attached. They usually occur when positioning modifiers (modifiers) on. Hirst lists 8 subclasses that relate to the classification of PPs, relative clauses, participles and adverbs. The friends you praise sometimes deserve it.
Gap finding and filling problems
occur when a 'moved out' constituent needs to be related to its 'original' position and there is more than one possible position.(Agricola did not deal with such ambiguities.) Those are the boys that the police debated ^ about fighting ^.
Analytical ambiguities
occur when a constituent can be analyzed in more than one way. Hirst presents 11 subclasses, ranging from simple word form MD (particle or preposition) to sentence type MD (question or prompt). Have the crystals dissolved? /!

Frequency of individual types

For the creation of NLP systems it would be useful to know the frequency of occurrence of the types of ambiguity in order to be able to deal with the most common ones using special methods. However, there are no publications on this - known to me - yet.

Agricola (p. 171) quotes Eggers (a study from 1964) who determined the following figures for the alternative `subject / direct object 'in German (see Type 42): From 745 sentences of popular scientific prose that contained subject and direct object ,

  • Both parts of the sentence were flexivically unambiguous in 46 sentences,
  • In 317 sentences, one of the two parts of the sentence was flexivically unambiguous
  • In 152 sentences the subject was determined by congruence with the predicate
  • In the remaining 230 sentences (31%), both parts of the sentence were ambiguous and this ambiguity could not be syntactically removed. Of these
    • For 208 the sequence `subject - direct object 'applied
    • For 22 the sequence `direct object - subject 'applied.

Currently A pilot study to determine MD frequencies is running at the University of Duisburg. A first result: (Email from Dr. S. Mehl, Dec. 13, 1995)

"So far, we have only analyzed a single phenomenon, namely PPs that appear after another PP or NP. This occurred 201 times in a corpus excerpt of 1125 sentences; 100 cases are complements or adjuncts to the verb, in 95 cases The PP referred to the immediately preceding noun, in 5 cases to the matrix noun of the preceding noun (ie NP -> N NP / PP PP), and in one case the PP referred to a subsequent adjective. "

Cognitive Aspects of Ambiguity

The ambiguity of a sentence does not necessarily correlate with difficulty in its cognitive reception. I.e. there is

  1. (syntactically) ambiguous sentences that are easy to process by humans, since a syntactic reading is largely masked out by semantic conditions or context. The woman sees the house.
  2. (syntactically) unambiguous sentences that are difficult for humans to process because they are e.g.
    • Wrong paths (garden-paths) contain: (p.50) Without her contributions would be inadequate. (p.53) We gave the man the grant proposal was written by last year a copy of this year's proposal. (p.55) Though George kept on reading the story really bothered him.
    • contain complex nested structures The man who completely renovated and sold the house, which stands on the edge of the forest of the 500-inhabitant village, has now been elected mayor,


Structural ambiguities occur in many ways in German. Their reasons lie mainly in ambiguous word forms and in ambiguous word sequences. Ambiguities are in principle language-specific, but a large number of the same MDs types can be identified in closely related languages ​​(such as German and English).

Knowledge of structural ambiguities can be used to

  • to translate certain types of MDs without resolution in machine translation.
  • to find statistically based heuristics for the resolution of structural MDs.
  • to find semantically based mechanisms for the resolution of structural MDs.
  • a (restricted) unambiguous language (controlled natural language), which increases the certainty of understanding (e.g. for the formulation of operating manuals).

Martin Volk
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