A language or a dialect?

In classic Baltic studies research it is often said that there are two Baltic languages in current usage: Lithuanian and Latvian. In this manner, Latgalian is treated as a dialect of the Latvian language. If Latgalian happens to be mentioned in a linguistic paper, it is usually followed by a passage “see: the Latvian language” (Price 2001: 286Price 2001 / komentarz/comment/r /
Price, Glanville (red.) 2001. Encyclopedia of the Languages of Europe. Oxford: Blackwell.
), where Latgalian is described as one of its dialects, mostly under a name of ‘Upper Latvian dialect’ or ‘Eastern Latvian dialect’ (Lewis 2009: 560Lewis 2009 / komentarz/comment/r /
Lewis, Paul M. (red.) 2009. Ethnologue: Languages of the World. Dallas: Summer Institute of Linguistics.
). Balode and Holvoet (2001Balode & Holvoet 2001 / komentarz/comment/r /
Balode, Laimute & Axel Holvoet 2001. „The Latvian language and its dialects”, w: Ö. Dahl & M. Koptjevskaja-Tamm (red.) Circum-Baltic Languages. vol.1. Past and Present. Amsterdam: Benjamins. 3–40.
) say this of the Latgalian language: “This dialect is the basis of a regional written standard, sometimes referred to as »Letgalian language«” (Balode & Holvoet 2001: 17Balode & Holvoet 2001 / komentarz/comment/r /
Balode, Laimute & Axel Holvoet 2001. „The Latvian language and its dialects”, w: Ö. Dahl & M. Koptjevskaja-Tamm (red.) Circum-Baltic Languages. vol.1. Past and Present. Amsterdam: Benjamins. 3–40.
). Taking into account linguistic criteria, Latgalian is usually treated as a Latvian dialect. It is not, however, identical to Upper Latvian subdialects. Non-linguistic factors – above everything, the attitude of language users towards their own language – support the theory that Latgalian should be acknowledged as a separate language. (Nau 2011: 8Nau 2012 / komentarz/comment/r /
Nau, Nicole 2012. “Modality in an areal context: the case of a Latgalian dialect”, w: B. Wiemer i in. (red.) Grammatical replication and borrowability in language contact. Berlin: Mouton De Gruyter. 465–508.
).
Undoubtedly, the dialectological point of view supports the claim that Latgalian is a variant of the Latvian language, as well as, taking into account sociolinguistic aspects, that it is a separate language – and an important marker of identity for Latgalians.