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:
Texts discussing linguistic reconstruction commonly preface reconstructed forms with an asterisk (*) to distinguish them from attested forms.
An attested word from which a root in the proto-language is reconstructed is a reflex. More generally, a reflex is the known derivative of an earlier form, which may be either attested or reconstructed. Reflexes of the same source are cognates.
First, languages that are thought to have arisen from a common proto-language must meet certain criteria in order to be grouped together; this is a process called subgrouping. Since this grouping is based purely on linguistics, manuscripts and other historical documentation should be analyzed to accomplish this step. However, the assumption that the delineations of linguistics always align with those of culture and ethnicity must not be made. One of the criteria is that the grouped languages usually exemplify shared innovation. This means that the languages must show common changes made throughout history. In addition, most grouped languages have shared retention. This is similar to the first criterion, but instead of changes, they are features that have stayed the same in both languages.
Because linguistics, as in other scientific areas, seeks to reflect simplicity, an important principle in the linguistic reconstruction process is to generate the least possible number of phonemes that correspond to available data. This principle is again reflected when choosing the sound quality of phonemes, as the one which results in the fewest changes (with respect to the data) is preferred.