Unsolved problems in linguistics

This article discusses currently unsolved problems in linguistics.

Some of the issues below are commonly recognized as problems per se, i.e., it is general agreement that the solution is unknown. Others may be described as controversies, i.e., while there is no common agreement about the answer, there are established schools of thought that believe they have a correct answer.

Languages

 * Origin of language is the major unsolved problem, despite centuries of interest in the topic.
 * Unclassified languages (languages whose genetic affiliation has not been established, mostly due to lack of reliable data)
 * Special case: Language isolates
 * Gradient well-formedness, referring to intermediate linguistic phenomena falling between complete well-formedness and complete ill-formedness.


 * Undeciphered writing systems

Psycholinguistics

 * Language emergence:
 * Emergence of grammar
 * Language acquisition:
 * Controversy: infant language acquisition / first language acquisition. How are infants able to learn language? One line of debate is between two points of view: that of psychological nativism, i.e., the language ability is somehow "hardwired" in the human brain, and that of the "tabula rasa" or Blank slate, i.e., language is acquired due to brain's interaction with environment. Another formulation of this controversy is "Nature  versus nurture".
 * Is the human ability to use syntax based on innate mental structures or is syntactic speech the function of intelligence and interaction with other humans? The question is tightly related with the two major problems: language emergence and language acquisition.
 * The language acquisition device: How localized is language in the brain? Is there a particular area in the brain responsible for the development of language abilities, or is language not localized in the brain, or is it only partially localized?
 * What fundamental reasons explain why ultimate attainment in second language acquisition is typically some way short of the native speaker's ability, with learners varying widely in performance?
 * Animals and language: How much language (e.g. syntax) can animals be taught to use?
 * An overall issue: Can we design ethical psycholinguistic experiments to answer the questions above?

Translation

 * Is there an objective gauge for the quality of translation?
 * Machine translation, despite successes, is a source of a large number of unsolved problems
 * Pronoun resolution, Anaphora (linguistics)
 * Nominal compound analysis