Documentation

Studies.LevshinaEtAl2023

Levshina et al. (2023): Why We Need a Gradient Approach to Word Order #

This file formalizes the corpus illustrations of [LNAT+23]'s case for describing word order by continuous measures rather than categorical labels. The paper's two measures of a binary order are the proportion of one order and the Shannon entropy of the order in bits; the entropy is the entropy of the Bernoulli law of the order at that proportion (orderEntropy_eq_binEntropy), so it is 0 when one order is fixed and 1 at an even split, the worked values of section 4.1.1, and among languages that put the subject first more often than not it ranks languages in reverse of the proportion (orderEntropy_lt_iff). In the 31 news corpora of Figure 1 the subject precedes the object in most clauses of every language (subject_usually_first). Figure 3 plots the mutual information between case marking and syntactic role against order entropy for 30 corpora: the two covary positively over the sample (covariance_entropy_caseInformation_pos), the corpus of maximal entropy, Lithuanian, has the most informative case marking (freest_most_case_informative), and the corpus of minimal entropy has none (most_rigid_least_case_informative). The Russian register study of section 4.1.3 is the population of its 300 annotated clauses under the uniform measure: verb–object order is less probable in conversation than in fiction (conversation_lt_fiction) and equally probable in fiction and news (fiction_eq_news).

Implementation notes #

References #

Proportion and entropy of a binary order (sections 1.1 and 4.1.1) #

The proportion of clauses with the subject before the object.

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    The subject is first in more than half the clauses exactly when it is first in more clauses than the object.

    The law of subject–object order in a language's corpus, which puts the subject first with the observed proportion.

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      The paper's word-order entropy, the Shannon entropy of the order in bits.

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        Word-order entropy is the binary entropy of the proportion, in bits.

        An even split of the two orders has entropy 1.

        Among languages that put the subject first at least half the time, entropy ranks them in reverse of the proportion: the closer to an even split, the more variable the order.

        The subject–object proportions of Figure 1 #

        In every one of the 31 corpora the subject precedes the object in most clauses.

        Case marking against order entropy (Figure 3) #

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        The corpora of Figure 3.

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          noncomputable def LevshinaEtAl2023.entropy (i : Corpus) :
          ℝ

          The entropy of subject–object order in a corpus, in bits.

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            noncomputable def LevshinaEtAl2023.caseInformation (i : Corpus) :
            ℝ

            The mutual information between case marking and syntactic role in a corpus, in bits.

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              theorem LevshinaEtAl2023.covariance_entropy_caseInformation_pos :
              0 < ProbabilityTheory.covariance entropy caseInformation (ProbabilityTheory.uniformOn Set.univ)

              Over the 30 corpora, order entropy and case information covary positively, so freer order goes with more informative case marking.

              theorem LevshinaEtAl2023.freest_most_case_informative :
              ∃ (i : Corpus), (statistics i).language = "Lithuanian" ∧ (∀ (j : Corpus), entropy j ≤ entropy i) ∧ ∀ (j : Corpus), caseInformation j ≤ caseInformation i

              The corpus with the most variable subject–object order, Lithuanian, has the most informative case marking.

              The corpus with the most rigid subject–object order has case marking carrying no information about syntactic role.

              Register and modality in Russian (section 4.1.3) #

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              The annotated clauses, as a population.

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                The probability of verb–object order in a text type, under the uniform measure on the clauses.

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                  The probability of verb–object order in a text type is the share of its clauses in that order.

                  Each text type contributes one hundred clauses.

                  Verb–object order in 39 of the 100 conversational clauses.

                  Verb–object order in 83 of the 100 fiction clauses.

                  Verb–object order in 83 of the 100 news clauses.