Linguistics and Machine Translation

Transcription

1 Linguistics and Machine Translation Helge Dyvik University of Bergen A b stra c t This talk discusses some of the challenges posed for theoretical linguistics by translational problems. It briefly discusses different aspects of the concept of translational equivalence and the degree to which this relation may be captured by machine translation (MT) systems. It is argued that the formal requirements and multilingual perspective of MT provide new criteria o f adequacy for semantic theraies. This motivates further development of linguistic semantics as a prerequisite for a semantically based theory o f machine translation. In particular it seems that the semantics of translational equivalence needs to be able to refer to a typology of linguistic objects as part of its ontology. Some of the points are illustrated by a short presentation of an experimental MT project. Finally it is briefly indicated how the treatment of linguistic objects as part of the semantic model fits into a situation theoretic account 1. Translational Equivalence as Empirical Evidence A t least one optim istic thing can be said about the relationship b etw een linguistics and M T : it is im proving. T here w as a tim e w hen the tw o concepts w ere rarely conjoined, and if th ey w ere, b u t seem ed a m o te plausible conjunction than a n d. T o-day, how ever, both fields h ave changed som ew hat: linguistic theories o f gram m ar tend to take problem s o f com putational tractability seriously, and linguistic approaches are finding th eir w ay not only into sm all experim ental M T projects but also into the large m arket-oriented ones. W ithin this area o f increased interaction betw een the tw o fields the flow o f in form ation - o r inspiration - is usually seen as unidirectional: linguistic theories o f syntax and sem antics p rovide representational tools fo r the developers o f M T system s, but rem ain rath er u n perturbed by the activity them selves. H ow ever, the increased c o n ta a betw een linguistics and the activity o f tran s lation should not be seen as a pure case o f applied science, in w hich results from lin g u istics are sim ply used to solve practical problem s. T ranslation should also be recognized as an im portant testing ground fo r linguistics, reinforcing a m uch-needed m ultilingual perspective in the dev elo p m ent o f m o te o r less form al linguistic theories. Specifically, th e pre-th eo retic co n cep t o f translational equivalence m ay provide valuable criteria o f adequacy fo r lin g u istic theories. T h is is especially evident w ithin sem antics. W ithin linguistic sem antics w e try to characterize the m eaning o f a linguistic expression by translating it into som e m eaning representation. T h is m eaning representation is, basically, ju st another linguistic expression, and the natural question is how this alternative expression brings us clo ser to the characterization o f m eaning than did the original expression. 'There are several relationships a m eaning representation m ay e n te r in to w hich m ay 67, pages 67-78

2 m otivate it as an inform ative characterization o f m eaning. F o r one thing w e m ay relate it to different expressions w ithin the sam e language, fo r instance by m eans o f a m odel theoretic interpretation, thereby characterizing various sem antic relations like synonym y, entailm ent etc. betw een expressions; fo r an o th er the m eaning representation can be used to m ediate betw een language and other contacts w ith reality, like sight and action; fo r yet another the representation can be related to ex p ressio n s in different languages, and hence characterize sem antic relations across language borders. T h e relation o f translational equivalence involves ju st this last-m entioned type o f sem antic relations and hence constitutes an em pirical dom ain w ith respect to w hich sem antic representations need to b e adequate. T h e relation o f translational equivalence is not easy to pin dow n, but a corpus o f actual tex ts paired w ith th eir translations, sorted according to quality b y txlingual inform ants, w ould be a starting poin t, giving us p art o f the extension o f the relation, so to speak. T he translational relation is m anifested in such a collection o f actual translations. T o the extent that sem antic representations a re adequate w ith re s p e a to such p h e n o m e n a -th a t is, to tiie extent that they classify equiv alen t expressions to g eth er - they are also m otivated as som ething m ore than ju st arbitrary alternative encodings o f som e sem antic content. It is an age-old insight that translatiorud equivalence involves m uch m ore than denotational equivalence. G ani leaving aside now the im portant question o f w hether the translation relation should be conceived as an equivalence relation at all; w e m ay n o te that good translation is frequent! y assum ed to b e irreversible.) T h e literature o n translation discusses several sub-species o f the relation; the follow ing categories are suggested by W ern er K o ller (1983:186ff.): 1. D enotational equivalence 2. C onnotative equivalence 3. Text-ru>rmative equivalence 4. P ragm atic equivalence 5. F orm al equivalence D en o ta tio n a l equivalence m ean s equivalence w ith respect to properties o f a described situation (conceived as a section o f objective reality ). H ow ever, languages usually allow alternative verb alizin g strategies, w hich m ay induce different p ersp ectives on w hat m ay still be conceived as the sam e described situations, highlighting different aspects o f th eir tem poral structure o r o f the relationships b etw een th eir participants. (E xam ple: I can only stay until S P M vs. I have to leave at 5 P M.) S im ilarly, alternative verbalizations m ay belong to different sub-languages o r levels o f style. E quivalence w ith respect to such properties is co nnotative equivalence. T ext-norm ative equivalence is equivalence w ith respect to properties characteristic o f certain text types. A French business letter m ay have a different structure from a N orw egian business letter, a F rench/ N orw egian p a ir o f letters are text-norm atively equivalent only if they each satisfy the respective F rench and N orw egian conventions fo r such texts. P ragm atically equivalent texts o r utterances are eq u iv alen t w ith respect to the ctm nmunicative acts perform ed w ith them, and th eir effects on the receiv er (such as the degree o f politeness accom panying a request, irony, etc.). C ultural differences frequently m ak e the achievem ent o f pragm atic equivalence d iffic u lt F inally,/ort no/ equivalence is eq u iv alen ce w ith respect to properties o f assonance, rhym e, rhythm and w ord-play. O bviously, all these ty p es are n o t alw ays o f equal im portance, b u t they all belong in a principled discussion o f translational equivalence. W e m ay n o te th at denotational equivalence prim arily co n cern s the described situation, pragm atic equivalence th e discourse situation, w hereas connotative, text-norm ative and form al equivalence prim arily concern, in an irreducible w ay, the linguistic sig n s them selves. I f tw o texts are equivalent w ith respect to chosen perspectives, levels o f style, text-structural norm s and m etrical properties, they can be said to be equivalent w ith respect to the typ es o f lin g u istic d evices used in them. T his suggests that a precise characterization o f translational equivalence presupposes not only adequate denotational sem antics and pragm atics enabling us to 68 68

3 refer to such properties o f described situations and discourse situations w hich translationally equivalent expressions have to b ear a com m on relation to. It seem s th at w e also need a universal typology o f linguistic devices: linguistic expression types them selves are an irreducible p art o f the onto lo g y o f things w hich translationally equivalent expressions have to h ave in com m on. T h u s, form al aspects o f a text m ay create types o f m eaning th at w e w ant to re-create in a translation. If w e take it as axiom atic that it is the task o f sem antics to account fo r all aspects o f m eaning, these translational i^ e n o m e n a bring new problem s w ithin the scope o f sem antic theories. 2. Limits of MT: Equivalence from Pre-Established Correspondences T ranslational equivalence is basically a relation b etw een te xts o r u ttera n ces rath er th an betw een lexical and gram m atical elem ents in language descriptions. In o th er w ords, translational eq u iv a lence concerns p a ro le rath er than longue. It is an analytic task to reduce translational equivalence betw een texts, as far as possible, to a function o f correspondence relations b etw een elem en ts o f language descriptions - to relations o f langue rath er than p a ro le. H ow ever, it seem s very lik ely that there are types o f translational equivalence that cannot be so reduced. T h u s, w hile connotative properties o f individual lexem es m ight be given som e representation in th e lex ico n, it is difficult to see how inform ation about connotative and stylistic properties o f com plex [riirases can b e derived com positionally, in the w ay inform ation about d enotative properties are. In such cases the only solution seem s to be to list such com plex phrases w ith th eir properties as idiom s, but ex tensiv e use o f this solution is at least im practical because it leads to an explosion in th e in v en to ry o f idiom s. Furtherm ore, global stylistic properties o f texts that concern, fo r instance, th e frequency o f certain constructions cannot even in principle be reduced to sim ple correspondence relations betw een linguistic descriptions. T here are also aspects o f form al translational equivalence (fo r instance, in translations o f poetry) and culture-bound pragm atic equivalence th at seem to presu p p o se genuine creativity o n tiie part o f the translator, and hence to be som ething th at cannot b e reduced to pre-established correspondences. T hese lim itations are at the sam e tim e lim itations on the possibility o f m achine translation. A m achine translation system is possible to the extent that w e have been able to reduce aspects o f translational equivalence to functions o f pre-established correspondence relations b etw een finite linguistic descriptions. T h e linguistic analysis in the descriptions m ay show any d eg ree o f sophistication, and w e m ay grant the possibility that the translation algorithm is able to exploit contextual inform ation o f various kinds to choose am ong alternatives - the fact rem ains th at any equivalence betw een texts established b y the system m ust be com positionally derivable from th e elem en ts in the descriptions and the pre-established correspondence relations b etw een them. T h is hold s true w hether w e im plem ent the relations as sim ple p ointers o r as representations o f som e kind, representing w hat the corresponding entities have in cotiunon. S u ch representations, if w e u se them, can reasonably be seen as sem antic representations. S ince it seem s plausible to claim th at all aspects o f translational equivalence are m eaning related, it should be the task o f sem antics to acco u n t for the correspondence relations b etw een languages o n w hich translational equivalence is based. Sem antic representations, then, should csf)ture w h atever a translational eq u iv alen t h a s to be equivalent w ith respect to, to tiie extent th at th is is derivable from th e linguistic descriptions. S uch representations are at th e sam e tim e potential in terlin g u a exp ressio n s - it should in p rin cip le be possible to im plem ent a translation algorithm that translates a source tex t to such a representation, and generates a target text from it

4 3. InterUngua as a Theoretical Tool T h is does n o t m ean that it w ould be a good idea to d o so in practice. T he m ajority view is that the transfer technique is to be preferred o v er the interiingua technique, and there are often good argum ents to support this view. T h e goal o f constructing a tru e interiingua is often considered as unrealistic, o r at least im practical. Such a universal interm ediate representation is easily seen at least as a detour, in m any cases it seem s sim p ler to define direct transitions from source representations to targ et representations. Still, the idea o f an interiingua should n o t be discarded out o f hand. In the first place, th e possibility o f interlingua-based translation does not im ply the possibility o f a tru ly universal interiingua, com m on to all conceivable language pairs. A n interiingua can be specific to a g iven language p a ir and still be an interiingua. In the second place, w e should distinguish b etw een the theoretical p o ssib ility o f an interiingua and the p ra ctica l u tility o f having su ch an interiingua actually im plem ented in a system. E ven if w e decide against the latter, w orking o u t an in teriin g u a m ig h t be a useful p art o f a principled study o f translational equivalence. In f a a, o n reflection it is easily seen th at th e distinction betw een interiingua and transfer is not a deep distinction o f principle, but rather a fairly superficial o n e o f im plem entation. It is n ever die case th at transfer m u st t e preferred o v er interiingua because transfer is the only p o ssib le option: interiingua is possible w henever transfer is. M achine translation actually im plies th e possibility o f interlingua-based m achine translation. T h is is because m achine translation, as I have already pointed out, is only possible to the extent that translational equivalence can be reduced to a function o f pre-established correspondences betw een elem ents o f tw o language descriptions. Since the language descriptions are finite, there w ill be a finite n u m b er o f such pre-established correspondences. T h e correspondences can be im plem ented as sim ple pointers, but it is o f course also possible to label each correspondence w ith a unique nam e, and to w rite rules fo r com bining such labels com positionally in tandem w ith the rules fo r com bining the corresponding expressions syntactically. In short, the correspondence relations, being finite in num ber, can evidently be described in a m etalanguage. Such a m etalanguage w ould be a theoretically possible interiingua betw een the tw o languages, and even if w e d o n t im plem ent it as an interiingua the m etalanguage m ight be a useful theoretical tool fo r keeping o u r ideas straight w hile w riting the program s. 4. The PONS Project: Exploiting similarity between languages N o w, 1 h a v e n t w orked out such a theoretically interesting interiingua yet. I have, on the oth er hand, been w orking o n an experim ental translation system, and 1 should like to give a b rie f sketch o f it in o rd er to illustrate som e o f the points I have m ade. T h e project is called P O N S - acronym ic for P artiell O versettelse m ellom N s r s t^ n d e S p rik (Partial T ranslation betw een C losely R elated L anguages). T h e starting p o in t w as an id ea about studying som e aspects o f the relationship betw een linguistic m otivation and com putational tractability in M T system s. A com m on objection to lin g u istically sophisticated language descriptions as m odules in translation system s is that they w ill inevitably m ak e analysis and synthesis hopelessly redundant and inefficient, com frared to quick ad-hoc shortcuts from source construction to target construction, w ithout regard fo r th eir full set o f gram m atical and sem antic properties. T h is is evidently a valid consideration - it w ould be irrational to spend tim e finding a lo t o f gram m atical and sem antic inform ation if you really d o n t need i t O n th e o th er han d, lin g u istic m otivation and com putational tractability could be com bined if w e could achieve a linguistically w ell-inform ed system able to refrain from using all its know ledge all the tim e. If the system had som e m eans o f evaluating the com plexity o f a given translatioruil task in advance, it could in fer the am ount o f analysis required and adjust its m ode o f operation accordingly. T h e possibility o f taking shortcuts w ould obviously be m ost frequent during translation betw een closely related languages; hence it w as natural to try out these ideas in relation to translation betw een 70 70

5 a pair o f Scandinavian languages like N orw egian and S w edish. T h e form al to o ls o f unification gram m ar seem ed w ell suited to the task, since feature structures can be m ore o r less underspecified: inform ation can be rem oved from them as the need arises. It is not only considerations o f efficiency that m otivate such an attem pt to achieve a system that uses its know ledge in a considered w ay. It seem s quite plausible to assum e that h u m an translators behave in a sim ilar m anner. W e s e o n able to a d ^ t the am ount o f in form ation w e b rin g to b e a r on a problem to its com plexity. T hus it is obviously fa re a sie r fo r us to translate b etw een clo sely related languages than betw een languages that are genetically and typologically fu rth er apart. T h e S candinavian languages are alm ost lim iting cases in th is re s p e c t In translations b etw een D anish, Sw edish and N orw egian, o r b etw een BokmfU and N ynorsk, there w ill freq u en tly (but far from alw ays, o f course) be a w ord-by-w ord ty p e correspondence betw een source and targ et texts. A natural procedure in such cases w ould be first to inspect die so ite n c e to b e translated sufficiently closely to determ ine th at it contains no constructions departing from th e unm arked w ord-by-w ord case, and then translate w ord-by-w ord, m aking m orphological adjustm ents along th e w ay. T h e hum an translator w ould n o t take the trouble to reflect carefiilly and a t len g th o n th e content and connotations o f the source sentence, in abstraction from its syntactic form, and th en try to encode this content from scratch in the target language w ith n o regard fo r the w ay it w as expressed in the source text. O nly to the extent that the constructions d o n o t allow fairly sim ple form al m appings is such a closer consideration o f sem antic properties necessary. T h e tran slato r w ill use as m u ch o f the structure o f the source sentence as possible - as lo n g as she can tru st th at a sim ilar sentence structure in the target language is translationally equivalent. A nd this is n o t a case o f laziness; it is because this m ethod is a precondition fo r a good translation, th at is, a tran slatio n w h ich renders the properties o f the source text as reliably as possibly, in clu d in g its w a y o f using language. B y a w ay o f using language" 1 have in m ind production o f the type o f m eaning w hich is captured by connotative equivalence (such as equivalence w ith respect to the chosen perspective on a situation), pragm atic equivalence and form al equivalence. L anguages have different resources, different device inventories, fo r creating such m eaning - that is w hat m akes translation difticult - b u t the m ore closely tw o languages are related, the g reater the o v erlap b etw een th eir inventories o f linguistic devices w ill be. It is not a facile shortcut, but the satisfaction o f an independent purpose o f translation w hich takes place w hen w e choose equivalent linguistic devices in a tran slatio n - fo r instance w ord-by-w ord translation w henever that is possible. ( P o ssib le here m ean s p reserv in g translational eq u iv alen ce - including connotative equivalence etc. In o th er w ords, it is not a counter-argum ent to the claim m ade here that w ord-for-w ord translations frequently are bad - w hen they are bad, they presum ably are not th e closest possible equivalent.) In such cases w e p ass directly from a device in one language to an equivalent device in the other, careful consideration o f the actual jo b done by these devices is superfluous. T his does n o t m ean th at m ean in g suddenly is unim portant, it sim ply m eans th at equivalence o f m eaning has been established once and fo r all, given o u r know ledge o f the r e l a tio n ^ p betw een the languages, and therefore w e need n o t w orry about it every tim e. H ence there are both practical and theoretical reasons to try to d ev elo p a system able to take shortcuts past an involved sem antic analysis w henever this is possible because o f a c e rt^ n degree o f structural correspondence b etw een the tw o languages. T his is a basic idea in th e P O N S project. T h e system is im plem ented (in Interlisp), excep t fo r a few m odules th at are n o t fully i n t e g r t ^ y e t T he linguistic descriptions are developed w ithin an extended and m odified v ersio n o f L auri K arttunen s D -P A T R, a fh u n ew o ik fo r developing unification-based gram m ars. T h e id ea o f shortcuts is captured by a distinction betw een three different m odes o f operation, co rresp o n d in g to three different degrees o f correspondence betw een source and target constructions. W e w ill look at the m ost elaborate m ode. M ode 3, first

6 Fig. 1. The three modes o f PONS 72 72

7 Fig. 2 Situation schema, PONS version 5. Mode 3: Semantic Representations as Interlingua T he M ode 3 path from source string to targ et strings is described in the o u te r circle o f fig. 1. T h e language description o n w hich parsing is based consists o f a set o f annotated p h rase structure rules, a set o f stem s, in w hich each stem contains all inform ation w hich is com m o n to all form s o f that stem, and a set o f w ord form s containing further inform ation. All entities - rules, stem s an d w ord form s - are represented as feature structuius, o r directed graphs, w h id i are unified d u rin g parsing. T he result o f a p arse is a j^rrase structure tree and a feature structure. T h e feature structure consists o f substructures, one o f w hich is a sem antic representation in the form o f a situ a tio n sch em a (fig. 2). T h e situation schem ata I am u sin g are som ew hat m odified versions o f th e situation schem ata introduced by F enstad, H alvorsen, L angholm and van B enthem in A situation sch em a is a representational form at suited to be interpreted b y situation theory. In S itu atio n S em antics the m eaning o f a sentence is conceived as a relation b etw een types o f discourse situations and ty p es o f described situations: the m eaning constrains these situations to be o f certain types. T h e ex am p le in fig. 2 represents the sentence John left. In the schem a attributes represent param eters o f situations (a situation is constituted o f a relation, a set o f arg u m en ts to it and a location, am ong o th er things)

8 w hile v alues represent the corresponding entities in the situations represented. T he outennost lay er represents aspects o f the discourse situation, w hile the described situation is entered as the value o f arg3 (it is the entity about w hich the speaker inform s the hearer). In the full feature structure o f a sentence the situation schem a is inter-related w ith the syntax substructure in various w ays. Fig. 3 show s the basic layout o f full feature structures, w hile fig. 4 show s a sim plified exam ple..syntax tra n s Fig. 3 Basic layout of PONS feature structures T h e patterns o f unifications betw een the syntax and sem antics substructures express such things as linking relations b etw een syntactic functions and sem antic aig u m en t positions. In M ode 3 the situation schem a is extracted as a kind o f interlingua expression from the feature structure. In other w ords, lin k in g relations and o th er syntactic inform ation from the source string parse are forgotten about, since th ey are source language ^ c i f i c. T arg et strings are then generated from the situation schem a, on the b asis o f the target gram m ar, in three stages (cf. fig. 1, right-hand colum n o f boxes): 1. T arg et stem s expressing the relation values in the schem a are retrieved from the lexicon, and th eir feature structures are unified into th e situation schem a. T h e result is that target language sp ecific syntactic features are added, giving a set o f full feature structures, linking relations and all, as o u tp u t 2. S y n tactic rules are predicted top-dow n, the predictions being constrained and governed by the in form ation in th e feature structures, w hich in a sense k now all about the constructions about to be generated. T h e o u p u t is a set o f trees, w ith lexical stem s at the term inal nodes. 3. W ord form s are entered at the term inal tree nodes, to th e ex ten t th at th eir feature structures are co m p atib le w ith w h at is already there. T h e output is a set o f targ et strings - th e set o f strings, that is, to w hich the targ et g ram m ar assigns situation schem ata com patible w ith the source situation schem a. T o th e exten t th at I have been able to capture the properties diat defm e translational equivalence in the situation schem ata, the strings are useful translations

9 Fig. 4 Feature structure with interrelated syntax and irons substructures 75 75

10 6. Modes 1 and 2: Shortcuts by exploiting similarity T his, then, w as the m o st elaborate m ode. N ow let us consider the m odes that allow the system to explo it structural sim ilarities betw een the languages - m odes 1 and 2 in fig. 1. T h e idea is that the system itself should be able to decide th at th is chunk corresponds to a targ et construction w ord-by-w ord, and hence is to be tackled in M ode 1, w hereas th is chunk c o r t e ^ n d s in a slightly m o te in d irect fashion, w ith discrepancies in constituent o rd er and gram m atical form atives, and hence M o d e 2 is in order, w hile, finally, th is one does n o t correspond in any interesting w ay at all, so here w e have to reso rt to M ode 3 and retrieve a situation schem a. T h e basis fo r m aking such decisions w ill have to be language p a ir ^ c i f i c inform ation. A t th e outset, how ever, the language descriptions are independent o f any specific translation partner. T he languages are described in th eir o w n term s - excep t fo r the obvious fact th at the sam e gram m atical apparatus has been em ployed, ensu rin g th at the sam e type o f gram m atical phenom enon is described in the sam e term s in every language. B u t on the b asis o f such descriptions g ram m ar com parisons can be perform ed autom atically. A n algorithm has been im plem ented w hich to som e exten t pre-com piles gram m ar pairs: it com pares th e entities in the tw o gram m ars and the tw o lexicons and adds inform ation about the results o f the com parison to them. T h u s after the com parison the language descriptions will co n tain inform ation about th eir partners. L et us briefly co n sid er how this wiu be utilized in M ode 1 and M o d e 2. M ode 1 is the default m ode from w hich the system departs only w hen triggered to do so. It is the m o d e o f w ord-by-w ord correspondence. E ven so, som e syntactic analysis has to be perform ed, in o rd er to achieve disam biguation o f hom onym ous form s, and in o rd er to d etect cases w here M ode 1 is insufficient. T herefore a syntactic tree is derived. T h e rules and lexical entries utilized in this derivation w ill contain inform ation to the effect that an identical tree w ith the sam e com positional properties can be derived by the target language rules and lexical entries. T his m eans that w e do n o t need to do that: w hen the correspondence betw een source and target string is that close, w e can forget about th e target gram m ar; the source tree itse lf can be used. T h en the source lexical entries at the term inal nodes are replaced by corresponding target entries, w hereupon the resulting structure enters stage 3 o f the synthesis procedure (cf. fig. 1) during w hich com patible target w ord form s are found. T h is procedure w ill appropriately handle gender clashes and various kinds o f one-to-m any correspondences b etw een the tw o lexicons. M ode 2 is in o rd er in cases w here source and target strin g still correspond w ith respect to the sets o f sense-carrying w ords they contain, but d iffer in constituent order, in die presence o f sense-less gram m atical form atives, o r both. In this case the so u rce tree carm ot be used, but the source feature structure, including its gram m atical inform ation (its f-structure in LEG term s) is still useful. A n exam ple o f such a correspondence w ould be N o rw eg ian d en nye b ilen m in vs. S w edish m in n y a b il m y new c a r. T h e g ram m ar com parison h as identified cases w h ere a rule in one language corresponds to a rule in the o th er w ith respect to sense-carrying daughters and com positional properties, b u t not w ith respect to constituent o rd er o r sense-less daughters. In such cases pointers have been constructed betw een the rules. H ence the p rocedure is th at the system recognizes the pointer, retrieves th e target rule, overw rites its feature structure o v e r the source feature structure, and starts top-dow n prediction o f targ et rules constrained b y th e m odified source feature structure. In o th er w ords, it enters stage 2 o f th e full synthesis procedure. F in ally, M o d e 3 is triggered w hen th e parse reveals eith er a rule o r a lexical entry w ith n o M ode 1 o r M ode 2 conespcm dent in th e target language. T h is w as a very b rie f sketch o f a system w hich operates partly o n interlingua principles - in M ode 3 - and p artly o n tran sfer principles - in M odes 1 and 2. I have suggested that a sem antic representation ideally should be able to capture everything in term s o f w hich w e define translational equivalence (at least to the extent that such equivalence is reducible to p ie-established conesp o n

11 dences b etw een d e m e n ts in the language descriptions), and that su ch a sem antic lepiesen tatio n can be seen as a kind o f dieoretical inteilingua expression. H ow does this w ork out in th e case o f the kind o f equivalence relations that are captured in M odes 1 and 2? In M ode 1 w e utilize com m on tree structures in the tw o languages, in M ode 2 w e utilize com m on syntactic feature structures. In o th er w ords, in these m odes w e have equivalence w ith respect to types o f lin g u istic sig n s: th e sam e linguistic devices are em ployed. A s w e have seen, diis is one kind o f equivalence w e w ant to c ^ tu r e, since it is in v o lv ^ in achieving coim otadve and form al equivalence. B u t i f translational equivalence m ay involve such gram m atical equivalence, and sem antics is to characterize all aspects o f translational equivalence, th en so n a n tic s has to be able to refer to aspects o f gram m atical form. Is this reasonable? 7. Language as Part of the World Several situation sem anticists (R obin C ooper, Stanley P eters, Jean M arie G aw ro n ) have been w orking tow ards the developm ent o f a situation theoretic account o f g ram m ar itself. T h e problem s addressed by C o oper do n o t p ertain to translation, bu t rath er to the situation th eo retic characterization o f the inform ation states attainable by hum an and artificial inform ation processors. A gram m ar, according to h is analysis, is a relation betw een possible linguistic u tterances and possible types o f facts in the w orld around us. T h is is n o p lace to go into details; suffice it to sa y th a t this approach involves treating linguistic entities - w ords, sentence constructions, gram m atical categories etc. - as things in th e w orld along w ith o th er things that hum an b ein g s can talk about and relate to. T his is a desirable perspective; sem antics ought to be able to account fo r lan g u age as som ething w hich occurs in die sam e w orld as the one language relates to. and n o t as som ething occurring in a dom ain entirely o f its ow n. T h is is obviously necessary in o rd er to account sem antically fo r reflexive language use, th at is, use o f language to talk about lan g u ag e, in expressions like th e w ord h o rse, the expression you ju st used, th at w as a bad sentence, etc. A nother exam ple is the usual situation sem antic analysis o f nam es (fig. S). Fig. 5 Circular representation o f a name 77 77

12 T h e analysis specifies that a precondition for using the nam e to refer to an individual is that the individual enters into the relation n a m e d w ith the nam e itself. In o th er w ords, the nam e enters into the specification o f its ow n sem antics, as part o f the type o f described situation it relates to. There is an elem en t o f circularity in this. If w e interpret the feature structure as a representation o f the nam e itself, the result is that the feature structure w ill contain a circular path. In th is case the linguistic en tity itse lf occurs in its described situation, w hich is slightly special. B u t th e o ccu rren ce o f linguistic entities in disco u rse situ a tio n s is quite typical, o f course, and d iscourse situations are also p art o f w hat enters into th e specification o f linguistic m eaning in a situation theoretic fram ew ork. H ence the elem ent o f circularity could becom e quite w idespread if w e develo p th e situation theoretic account in som e detail: linguistic signs becom e essentially circu lar structures, containing them selves as constituents o f their sem antic su l^ a rts. T his is a consequence o f u nderstanding th e m eaning o f an expression as th e w ay it constrains the relation b etw een discourse situations in w hich it can b e used and objects it can describe. Intuitively, the circu lar structure expresses the fact th at an essential property o f any discourse situation in w hich sig n S is used, is th at S is a constituent in it. A consequence o f th is is that if w e assum e th at trandatio n al equivalence is to m ean equivalent situation schem ata, then a sign w ill only be translationally equivalent w ith itself. T h is captures in a fairly brutal w ay the u n ique, non-translatable character o f linguistic signs: the insigfit o f m any translators th at th e perfect translational equivalence relation across languages is em pty. W hat we d o in practice is search fo r target expressions that are equivalent w ith re s p e a to su b sets o f the in form ation in the schem ata. In fact, I believe that w e do w ant a theory o f translation that accounts fo r its basic im possibility, w hile at the sam e tim e allow ing fo r various approxim ations to the unattainable ideal. C onsiderations like these m ight be a starting point for developing a sem antic theory o f translation - a study o f th e sem antics o f translation rather than sim ply w o tid n g w ith sem antics fo r translation. A s I have stressed, the theoretical constructs o f such a theory are not necessarily to be taken as m o d els fo r d ir e a im plem entation, but they m ight still provide the w ork w ith som e theoretical basis. 8. References C ooper, R. 1989: Inform ation and G ram m ar, unpublished m anuscript. D yvik, H elge 1990: T he P O N S P roject. F ea tu res o f a T ranslation System. Skriftserie, nr. 39, D epartm ent o f L inguistics and Phonetics, U niversity o f B ergen. F enstad, J.E., P.-K. H alvorsen, T. L angholm and J. v B enthem 1987: S itu a tio n s, Language and L o g ic. D ordrecht: R eidel. G aw ro n, J.M., and S. P eters 1990: A naphora a n d Q uantification in S itu a tio n Sem antics. C SLI L ectu re N o tes N u m b er 19, C enter fo r th e Study o f L anguage and Inform ation, Stanford. R o ller, W. 1983: E in fiih run g in d ie O bersetzungsw issensdurft, H eidelberg: Q uelle & M eyer. H elg e D yvik D epartm ent o f L in g u istics and P honetics U niversity o f B ergen S ydnesplass 9 N B ergen, N orw ay T el E -m ail d yvik@ hf.uib.no 78 78