Immediate constituent analysis


In linguistics, immediate constituent analysis or IC analysis is a method of sentence analysis that was first mentioned by Leonard Bloomfield and developed further by Rulon Wells. The process reached a full-blown strategy for analyzing sentence structure in the early works of Noam Chomsky. The practice is now widespread. Most tree structures employed to represent the syntactic structure of sentences are products of some form of IC-analysis. The process and result of IC-analysis can, however, vary greatly based upon whether one chooses the constituency relation of phrase structure grammars or the dependency relation of dependency grammars as the underlying principle that organizes constituents into hierarchical structures.

IC-analysis in phrase structure grammars

Given a phrase structure grammar, IC-analysis divides up a sentence into major parts or immediate constituents, and these constituents are in turn divided into further immediate constituents. The process continues until irreducible constituents are reached, i.e., until each constituent consists of only a word or a meaningful part of a word. The end result of IC-analysis is often presented in a visual diagrammatic form that reveals the hierarchical immediate constituent structure of the sentence at hand. These diagrams are usually trees. For example:
This tree illustrates the manner in which the entire sentence is divided first into the two immediate constituents this tree and illustrates IC-analysis according to the constituency relation; these two constituents are further divided into the immediate constituents this and tree, and illustrates IC-analysis and according to the constituency relation; and so on.
An important aspect of IC-analysis in phrase structure grammars is that each individual word is a constituent by definition. The process of IC-analysis always ends when the smallest constituents are reached, which are often words. The process is, however, much different in dependency grammars, since many individual words do not end up as constituents in dependency grammars.

IC-analysis in dependency grammars

IC-analysis is much different in dependency grammars. Since dependency grammars view the finite verb as the root of all sentence structure, they cannot and do not acknowledge the initial binary subject-predicate division of the clause associated with phrase structure grammars. What this means for the general understanding of constituent structure is that dependency grammars do not acknowledge a finite verb phrase constituent and many individual words also do not qualify as constituents, which means in turn that they will not show up as constituents in the IC-analysis. Thus in the example sentence This tree illustrates IC-analysis according to the dependency relation, many of the phrase structure grammar constituents do not qualify as dependency grammar constituents:
This IC-analysis does not view the finite verb phrase illustrates IC-analysis according to the dependency relation nor the individual words tree, illustrates, according, to, and relation as constituents.
While the structures that IC-analysis identifies for dependency and constituency grammars differ in significant ways, as the two trees just produced illustrate, both views of sentence structure are acknowledging constituents. The constituent is defined in a theory-neutral manner:
This definition is neutral with respect to the dependency vs. constituency distinction. It allows one to compare the IC-analyses across the two types of structure. A constituent is always a complete tree or a complete subtree of a tree, regardless of whether the tree at hand is a constituency or a dependency tree.

Constituency tests

The IC-analysis for a given sentence is arrived at usually by way of constituency tests. Constituency tests identify the constituents, large and small, of English sentences. Two illustrations of the manner in which constituency tests deliver clues about constituent structure and thus about the correct IC-analysis of a given sentence are now given. Consider the phrase The girl in the following trees:
The acronym BPS stands for "bare phrase structure", which is an indication that the words are used as the node labels in the tree. Again, focusing on the phrase The girl, the tests unanimously confirm that it is a constituent as both trees show:
Based on these results, one can safely assume that the noun phrase The girl in the example sentence is a constituent and should therefore be shown as one in the corresponding IC-representation, which it is in both trees. Consider next what these tests tell us about the verb string is happy:
The star * indicates that the sentence is not acceptable English. Based on data like these, one might conclude that the finite verb string is happy in the example sentence is not a constituent and should therefore not be shown as a constituent in the corresponding IC-representation. Hence this result supports the IC-analysis in the dependency tree over the one in the constituency tree, since the dependency tree does not view is happy as a constituent.
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