Linguistic reconstruction is the practice of establishing the features of an unattested ancestor language of one or more given languages. There are two kinds of reconstruction:

• Internal reconstruction uses irregularities in a single language to make inferences about an earlier stage of that language – that is, it is based on evidence from that language alone.
• Comparative reconstruction, usually referred to just as reconstruction, establishes features of the ancestor of two or more related languages, belonging to the same language family, by means of the comparative method. A language reconstructed in this way is often referred to as a proto-language (the common ancestor of all the languages in a given family); examples include Proto-Indo-European, Proto-Dravidian, etc.