Contains reports on two research projects.National Science Foundatio

Applegate, J. R.

Matthews, G. H.

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XVII. MECHANICAL TRANSLATIONV. H. Yngve A. N. Chomsky G. H. MatthewsJ. R. Applegate D. A. Dinneen A. B. PhillipsJ. L. Bennett Muriel Kannel Rosemarie StriussniggJ. S. Bross E. S. Klima J. J. ViertelElinor K. Charney K. C. Knowlton Ruth V. WardD. LiebermanA. TRANSLATION STUDIES. I.Communication between speakers of different dialects of the same language sharesfeatures with communication between speakers of different languages. In both cases,some translation is necessary. In communication between speakers of the same language,structural similarities may account for the fact that translation is less complex and maybe carried on by the hearer. As structural differences increase, the process becomesmore complex until an intermediary must be used. In this study an attempt was made todetermine the points of structural divergence that have the greatest effect on communi-cation.The subjects of this case study were three brothers who were four, five and one-half,and eight and one-half years old when the study began. They are the sons of native-bornparents whose speech is typical of the small New England community near Boston wherethey live. Deviations from the speech of the adult community were readily apparent in thespeech of all three children. The two younger children spoke a dialect that was almostcompletely unintelligible to adults (even, at times, to their parents). Yet they were ableto communicate freely with each other and with their playmates, and with their olderbrother. He spoke a dialect that could be clearly recognized as a form of the communitydialect with various distortions. The most obvious of these was severe stuttering;another was the reversal of the order of syntactic constituents.A description of the younger children's dialect shows that the difference between itand the adults' dialect can be traced to two phonological rules found in the children's dia-lect but not in that of the adults. Application of the first of these rules converts all frica-tives to stops; and application of the second converts any stop repeated within wordboundaries to a glottal stop. These two rules, when applied in the proper order (appli-cation of the second must precede application of the first), are sufficient to explain thedifferences between the two dialects. The apparent differences in morphology can betraced to these rules.A possible reason for the preservation of a deviant form of speech by the youngerchildren was that the oldest child, who understood them but whose speech was closer tothat of the adult community, was willing to act as a translator for them. Usually, aThis work is supported in part by National Science Foundation.223(XVII. MECHANICAL TRANSLATION)child's speech is considered a deviant form of adults' language, and he is required toalter it until it conforms to the pattern of the adults' language. This is necessary if heis to be understood. This was not true in this case, however. The fact that the oldestchild was able to serve as a translator when communication between the younger child-ren and adults broke down minimized the pressure to alter their speech so that theywould be understood.The translation of the younger children's utterances required only the elimination ofthe two special phonological rules that were peculiar to their speech. Apparently, theoldest child understood this. When he translated, however, the deviations that werecharacteristic of his speech in free conversation disappeared. There was no stutteringand no reversal of sentence constituents. This was true only when the translation wasgiven as a direct quotation ("He said, 'I want some candy!' "). When the translation waschanged to an indirect quotation ("He said that he wanted some candy"), the deviationsreturned.These facts suggest that the three-stage translation model, which consists of (a) anal-ysis of input sentence to obtain a structural specifier, (b) conversion of this specifier toa corresponding one for the output sentence, and (c) construction of the output sentence,may not be entirely accurate. In this case study, the generation of the output sentenceby the oldest child proceeded in quite a different way from the usual generation of sen-tences. If it had not, the translations would have shown the deviations that were char-acteristic of his speech in other situations. Other studies of translation may lead to abetter description of the translation process itself.J. R. ApplegateB. RECOGNITION OF THE STRUCTURE OF SENTENCESThe grammar of a natural language can be thought of as a finite list of ordered ruleswhich is such that the application of any particular set of these rules produces a sen-tence of the language. Some of the rules are optional recursive rules; that is, there isno limitation on the number of times that they may be applied in the production of a sen-tence. Thus, there is no limit on the number of different sentences that a grammar canproduce. Other rules are optional but not recursive; that is, they may be applied onlyonce. Still other rules are obligatory; they must be applied in the production of everysentence. A grammar of this type can be viewed as a certain function that has a vari-able for each optional rule of the language, and the order of these variables is the sameas the order of the rules. The values of the variables are numerals representing thenumber of times that the corresponding rule is applied. There are some sets of rulesin the grammar, all the members of which are optional, but no more than one of whichcan be used in the production of any one sentence. In such cases, a single variable can224(XVII. MECHANICAL TRANSLATION)represent the whole set of rules, and its value indicates which rule of the set is to beapplied. In this way a one-to-one correspondence between the combinations of values-which will hereafter be called "specifiers" -and the sentences of the language is estab-lished, and thus the sentences are denumerable.In addition, the sentences of a language can be placed in a well-ordering withoutaccumulation points. This ordering is given to the specifiers by assigning a number toeach specifier in the following way. All of the possible combinations of recursive rulesof the grammar are well-ordered by the diagonal method, and these combinations aremapped onto the positive integers. The positive integer that corresponds to the combina-tion of recursive rules in the specifier is placed in the leftmost place in the numberassigned to that specifier. Those values in the specifier that refer to nonrecursive rulesare placed to the right of this, in the same order that they have in the specifier. Thereis then a one-to-one correspondence between specifiers and their assigned numbers.Each place in these numbers has a different base, but only the leftmost place has infinityfor its base. These numbers can be put in numerical order-and therefore the specifiersassigned to them-and hence the sentences corresponding to the specifiers can be giventhe same order.Let us return to the examination of the grammar rules. Nearly all of the rules in agrammar have the characteristic of either keeping constant or increasing the number ofsymbols in the sentence that is being produced. A few of the rules decrease the numberof symbols by deleting some of them. For each of these rules that delete symbols thereis a maximum number of symbols that can be deleted. Furthermore, there is only asmall number of combinations of these rules that can be applied in the production of asentence. This means that, given a sentence that is n symbols long, a constant k canbe calculated with the characteristic that, in the production of the sentence, before theapplication of those rules that delete symbols, there will be no more than (n+k) symbolsin the sentence.Since grammar rules (with the exception of the deletion rules) either maintain thenumber of symbols in the sentence or increase their number, and since, in the numericalvalues that are given to grammar rules, a lower numeral represents a fewer number oftimes that the rule is applied, we conclude that, in general, the order of sentences isfrom shorter to longer. Furthermore, this order is roughly equivalent to the intuitivenotion of from less complex to more complex because, in general, the complexity of asentence increases with the number of times a recursive rule is applied in its production,for it is by such rules that clauses are added to a sentence and the relationship betweenclauses established. Therefore, given any number m, it is possible to calculate a spec-ifier in the order of specifiers which is such that there will be no specifier following itthat corresponds to a sentence of m symbols or less. Thus, the grammar of a naturallanguage is a decidable theory. To decide whether a given string of symbols is a sentence225(XVII. MECHANICAL TRANSLATION)of a certain language, one calculates the maximum number of symbols there would havebeen if no deletion rules had been applied in its production and then produces all the sen-tences of the languages which have that maximum number of symbols, or less, using theorder of the specifiers to be sure that every sentence of that set is actually produced justonce. All of these sentences will be produced in a finite time because there are no accu-mulation points in the order of specifiers. If one of the sentences matches symbol-for-symbol the string in question, then that string is a sentence of the language. Anotherfeature of this decision procedure is that for each possible derivation of a given stringof symbols, the decision procedure will produce a sentence that matches the string,symbol-for-symbol, and, because of the particular relationship between the specifiersand the grammar of the language, the specifier used in producing each sentence will bean unambiguous representation of the derivation of the sentence-that is, the grammati-cal analysis of the sentence.I shall now define the notion "linguistically significant class of sentences. " A classof sentences is linguistically significant if, in producing the members of this class, thesame grammar rule has been applied the same number of times to all of them. This isa generalization of the intuitive notion, "sentence type. " The specifiers for the membersof a linguistically significant class are alike in that the same numeral occurs in the placethat corresponds to the particular defining rule; this numeral represents the number oftimes that the rule is applied. In addition, the logical product of two linguistically signi-ficant classes of sentences, if it is nonempty, is also a linguistically significant class,and the specifiers for such a class will have more than one place containing the samenumeral. Note that if the product of two classes is empty, it would be because eachclass would have kept the same rule constant but at a different number of times. Thecorresponding class of specifiers would be a class all of whose members simultaneouslyhave two values in the same place-an impossibility.These considerations are of importance in the general problem of the recognition ofsentences, whether it be for a mechanical recognition procedure, such as those proce-dures that are being investigated by various mechanical-translation and information-retrieval projects, or for an explanation of how human beings use language. The closerelationship among the notion "linguistically significant class of sentence," the grammarof the language, and the decision procedure that automatically provides a proof for thesentence in question, suggests a method by which the recognition procedure might becarried out in a practical manner. The input sentence and its environment are examinedfor clues that would place it in some linguistically significant class of sentences. Thisclass is easily defined by a specifier in which some of the variables are left unspecified.The decision procedure uses this partially specified specifier to discover all of thosemembers of this class of sentences that match the input sentence symbol-for-symbol,and provides all of the grammatical analyses of the input sentence. Those sentences226(XVII. MECHANICAL TRANSLATION)that are produced by the decision procedure but do not match the input sentence can beused to reduce the number of sentences of the class that still must, in fact, be produced,for each of them can define a class of sentences having the characteristic of overlappingwith the class that is being produced but not of including the input sentence.G. H. Matthews2 27

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