Predicative Adjectives: An Unsupervised Criterion to Extract Subjective Adjectives

Proceedings of NAACL-HLT 2013, pages 534–539, Atlanta, Georgia, 9–14 June 2013. c⃝2013 Association for Computational Linguistics Predicative Adjectives: An Unsupervised Criterion to Extract Subjective Adjectives Michael Wiegand Spoken Language Systems Saarland University michael.wiegand@lsv.uni-saarland.de Josef Ruppenhofer Dept. of Information Science and Language Technology Hildesheim University ruppenho@uni-hildesheim.de Dietrich Klakow Spoken Language Systems Saarland University dietrich.klakow@lsv.uni-saarland.de Abstract We examine predicative adjectives as an unsu- pervised criterion to extract subjective adjec- tives. We do not only compare this criterion with a weakly supervised extraction method but also with gradable adjectives, i.e. another highly subjective subset of adjectives that can be extracted in an unsupervised fashion. In or- der to prove the robustness of this extraction method, we will evaluate the extraction with the help of two different state-of-the-art senti- ment lexicons (as a gold standard). 1 Introduction Since the early work on sentiment analysis, it has been established that the part of speech with the highest proportion of subjective words are adjec- tives (Wiebe et al., 2004) (see Sentence (1)). How- ever, not all adjectives are subjective (2). (1) A grumpy guest made some impolite remarks to the insecure and inexperienced waitress. (2) The old man wearing a yellow pullover sat on a plastic chair. This justifies the exploration of criteria to automati- cally separate the subjective adjectives from the non- subjective adjectives. In this work, we are interested in an out-of- context assessment of adjectives and therefore eval- uate them with the help of sentiment lexicons. We examine the property of being a predicative adjec- tive as an extraction criterion. Predicative adjectives are adjectives that do not modify the head of a noun phrase, but which predicate a property of the refer- ent of a noun phrase to which they are linked via a copula or a control predicate (3). We show that adjectives that frequently occur as predicative adjectives are more likely to convey sub- jectivity (in general) than adjectives that occur non- predicatively, such as the pre-nominal (attributive) adjectives (4). A subjective adjective may occur both as a predicative (3) and a non-predicative (5) adjective and also convey subjectivity in both con- texts. However, a large fraction of non-subjective adjectives do not occur as predicative adjectives (6). (3) Her idea was brilliant. (4) This is a financial problem. (5) She came up with a brilliant idea. (6) ?The problem is financial. 2 Related Work The extraction of subjective adjectives has already attracted some considerable attention in previous re- search. Hatzivassiloglou and McKeown (1997) ex- tract polar adjectives by a weakly supervised method in which subjective adjectives are found by search- ing for adjectives that are conjuncts of a pre-defined set of polar seed adjectives. Wiebe (2000) in- duces subjective adjectives with the help of distribu- tional similarity. Hatzivassiloglou and Wiebe (2000) examine the properties of dynamic, gradable and polar adjectives as a means to detect subjectivity. Vegnaduzzo (2004) presents another bootstrapping method of extracting subjective adjectives with the help of head nouns of the subjective candidates and distributional similarity. Baroni and …

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