[2] Moreover, a group of lects that are not considered separate languages, such as the members of a dialect cluster, may also be described as descending from a unitary proto-language.
It is by definition a linguistic reconstruction formulated by applying the comparative method to a group of languages featuring similar characteristics.
The comparative method, a process of deduction, begins from a set of characteristics, or characters, found in the attested languages.
If the entire set can be accounted for by descent from the proto-language, which must contain the proto-forms of them all, the tree, or phylogeny, is regarded as a complete explanation and by Occam's razor, is given credibility.
For example, lexical items that are loans from a different language do not reflect the phylogeny to be tested, and, if used, will detract from the compatibility.
In a few fortuitous instances, which have been used to verify the method and the model (and probably ultimately inspired it[citation needed]), a literary history exists from as early as a few millennia ago, allowing the descent to be traced in detail.
Likewise, Proto-Norse, the ancestor of the modern Scandinavian languages, is attested, albeit in fragmentary form, in the Elder Futhark.
Kortlandt (1993) offers several examples in where such general assumptions concerning "the nature of language" hindered research in historical linguistics.
[8] Ferdinand de Saussure would even express a more certain opinion, completely rejecting a positive specification of the sound values of reconstruction systems.
Even the widely studied proto-languages, such as Proto-Indo-European, have drawn criticism for being outliers typologically with respect to the reconstructed phonemic inventory.
In the same vein, Julius Pokorny in his study on Indo-European, claims that the linguistic term IE parent language is merely an abstraction, which does not exist in reality and should be understood as consisting of dialects possibly dating back to the paleolithic era in which those dialects formed the linguistic structure of the IE language group.