Difficulties for Machine Translation Systems

2.4.3 Syntactic and Semantic DifficultiesFurthermore machine translation is hard because relations between words and sentences pose a problem.  Inter- and Intrasentential RelationsTranslations of English texts into German or French, for example, require a distinction between different articles and genders. There is a popular example which illustrates this complexity in language because of pronouns: "The police refused the students a permit because they feared violence." or "The police refused the students a permit because they advocated violence." Human translators have to ask themselves the question, too, whether "they" refers to "The police" or "the students". The machines' analysis of the sentence may result that  "they" is a plural pronoun and can be feminine as well as masculine. When translating the sentence into German the system is lucky because the German plural noun is also independent of the gender. In French however, the police is feminine and the term "the students" is masculine. The translation of this sentence actually requires knowledge about students, police and students to realise the right relation between the words and to translate the pronoun correctly, so the system is expected to fail in this case. As you can imagine, intersentential (pronominal) references describe a more serious obstacle. Distinction between Word FunctionsBut even parsing a apparently simple sentence like "Flying planes can be dangerous." causes troubles for automatic translation services. Either "Flying" is a gerund noun and consequently the subject of the sentence or it plays the part of a present participle like an adjective to "planes". There is no additional clue which makes the system able to make the right decision or that helps the translator distinguishing between the word's different functions in the sentence.
This disability of analysing the context, references and relations is one reason why machine translation systems are useless for poetry and texts with complex structures and relations ranging more than one simple sentence. At the moment a solution for automatic translation systems is beyond the range of vision.