List of unsolved problems in linguistics

This article discusses currently unsolved problems in linguistics.

Some of the issues below are commonly recognized as unsolved problems; i.e. it is generally agreed that no solution is known. Others may be described as controversies; i.e. although there is no common agreement about the answer, there are established schools of thought that believe they have a correct answer.


  • Is there a universal definition of word?
  • Is there a universal definition of sentence?
  • Are there any universal grammatical categories?
  • Is syntactic structure constructed of part-whole relations of syntactic constituents or is it built of an asymmetrical dependency relation between words?
  • Can the elements contained in words (morphemes) and the elements contained in sentences (words or syntactic constituents) be shown to follow the same principles of combination?
  • How are domains for phonological processes related to syntactic structure? Do prosodic domains deviate from syntactic constituent structure?
  • Is it possible to formally delineate languages from each other? That is to say, is it possible to use linguistic (rather than social) criteria to draw a clear boundary between two closely related languages with a dialect continuum between their respective standard forms (e.g. Occitan and Catalan)?
  • How does grammaticalization function?
  • What constitutes grammatically correct language, as viewed by native speakers of that particular language, i.e. the problem of gradient well-formedness?
  • Is there one universal process with which the evolution of creole languages can be tracked?
  • How does lexical substitution function given the potentially limitless number of different contexts, the limits of one's knowledge and the limits of one's understanding and usage of language?
  • How do idiolects and dialects emerge? Are there any common patterns in their development? Can they be quantitatively and qualitatively measured at all and if so, how?

Philosophy of language

Historical linguistics and the evolution of language

The evolution of language

  • How and when did language originate?[1][2][3][4][5]
    • How and when did different modes of language (spoken, signed, written) originate?
    • Were Homo sapiens the first humans to use language? What about other species in the genus Homo?
    • Is language continuous or discontinuous with earlier forms of communication? Did language appear suddenly or gradually?

Language classification

  • What language families are valid?
  • Can any of the approximately 100 unclassified languages be classified?[6] Or does our limited knowledge of them prevent that?
  • Can we decipher any of the extant undeciphered writing systems?
  • Language isolates have no demonstrated relatives, and essentially form language families on their own. Can any of the approximately 159 language isolates be shown to be related to other languages?[7]
  • Can we use the comparative method to reconstruct back to an arbitrary time depth, or do we need new methods to reconstruct the distant past of languages? Is there a time depth beyond which we cannot reconstruct?
  • Can we ever demonstrate that all languages are ultimately related to each other, or that they aren't?


  • Language emergence:
  • 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 closely related to those of language emergence and 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 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?
    • What are the optimal ways to achieve successful second-language acquisition?
    • Animals and language: How much human language can animals be taught to use? How much of animal communication can be said to have the same properties as human language (e.g. compositionality of bird calls as syntax)?[9]
    • What role does linguistic intuition play, how is it formed and how does it function? Is it closely linked to exposure to a unique set of different experiences and their contexts throughout one's personal life?


  • How to deal with variation in language (including idiolects, dialects, sociolects, jargons, argots, etc.) to achieve effective and successful communication between individuals and between groups, i.e. what are the best ways to ensure efficient communication without misunderstandings: in everyday life and in educational, scientific and philosophical discussions?
  • What are the best ways to quantitatively and qualitatively compare linguistic competence and linguistic performance between individuals and between groups?
  • How does time (and the semantic change that it brings) and physical age influence linguistic competence?
  • How are argots formed, how do they function and what are the best ways to become proficient in an argot?
  • What causes linguistic features to begin to undergo language change at some points in time and in some dialects but not others?

Computational linguistics

  • Is perfect computational word-sense disambiguation attainable by using software? If yes, how and why? If no, why? (This presupposes the solution to the unsolved problems in the other areas of linguistics as a basis.)
  • Is accurate computational word-sense induction feasible? If yes, how and why? If not, why?

Lexicology and lexicography



  • Is there an objective way to determine which are the most difficult languages?
  • To what extent are conlangs usable and useful as used as natural languages by humans?


  1. Givon, Talmy; Bertram F. Malle (2002). The Evolution of Language Out of Pre-language. John Benjamins. ISBN 1-58811-237-3.
  2. Deacon, Terrence (1997). The Symbolic Species: The Co-evolution of Language and the Brain. W.W. Norton. ISBN 0-571-17396-9.
  3. MacNeilage, Peter, 2008. The Origin of Speech. Oxford: Oxford University Press.
  4. Botha, R. and C. Knight (eds) 2009. The Cradle of Language. Oxford: Oxford University Press.
  5. Dor, D., C. Knight & J. Lewis (eds), 2014. The Social Origins of Language. Oxford: Oxford University Press.
  6. Harald Hammarström; Robert Forkel; Martin Haspelmath (2019). "Glottolog 4.0: Unclassifiable". Jena: Max Planck Institute for the Science of Human History. Retrieved 2019-11-24.
  7. Lyle Campbell, ed. (2018). Language Isolates. Routledge Language Family Series. London and New York: Routledge. p. 11. ISBN 978-1-138-82105-7.
  8. "Simulated Evolution of Language: a Review of the Field", Journal of Artificial Societies and Social Simulation vol. 5, no. 2
  9. Suzuki, Toshitaka N.; Wheatcroft, David; Griesser, Michael (2018). "Call combinations in birds and the evolution of compositional syntax". PLOS Biology. doi:10.1371/journal.pbio.2006532.
  10. Robert Spence, "A Functional Approach to Translation Studies. New systemic linguistic challenges in empirically informed didactics", 2004, ISBN 3-89825-777-0, thesis. A pdf file Archived 2006-05-06 at the Wayback Machine
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