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In page List of unsolved problems in linguistics:

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  • 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?[2]
  • 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?