Nevertheless, differences do exist: the accent of a Valencian is recognisable, there are differences in subjunctive terminations, and there are a large number of words unique to Valencian; but those differences are not any wider than among North-Western Catalan and Eastern Catalan. In fact, Northern Valencian (spoken in the Castelló province and Matarranya valley, a strip of Aragon) is more similar to the Catalan of the lower Ebro basin (spoken in southern half of Tarragona province and another strip of Aragon) than to apitxat Valencian (spoken in the area of L'Horta, in the province of Valencia).
The Valencian language has often been seen as a dialect of Catalan due to their mutual intelligibility. However, the issue of language versus dialect is as much a matter of politics as of linguistics. By the criterion of mutual intelligibility, Valencian and other varieties of Catalan are dialects of a single language; but according to this criterion, Galician and Portuguese are also dialects of the a single language, a contentious conclusion; a similar argument can be made about the Scandinavian languages, especially Norwegian and Swedish. A language is defined by several factors, political ones among others.
What gets called a language is defined in part by mutual comprehensibility, but also by political and cultural factors. Historically, the perceived status of Valencian as merely a "dialect of Catalan" has had important political implications including bolstering Catalan nationalism and the idea of the països catalans or "Catalan countries." Conversely, many Valencians who advocate distinguishing the languages do so to resist a perceived Catalan nationalist agenda aimed at absorbing Valencian language and identity, and incorporating Valencians into a constructed nationality centered in Catalonia.
The concept of a "linguistic Catalan diasystem" was developed at the beginning of the 20th century as part of Catalan nationalist discourse; prior to that, Catalan was generally considered a dialect of Occitan and was included in the "linguistic Romanic-Occitanian diasystem". This newer "linguistic Catalan diasystem" would incorporate Valencian into the Catalan system, instead of both Catalan and Valencian being considered as dialects under the former "Romantic-Occitanian diasystem." This system brings Catalan nationalism the benefit of an increase in the official number of Catalan speakers. The term "Western Catalan" ("catalá occidental") was developed as part of this discourse, based on some lexical and phonetic similarities that the speech of the zone of Lleida (Lérida) had with that of Valencia.
Similarly to Serbian and Croatian, the issue of whether Catalan and Valencian constitute different languages or merely dialects has been the subject of political agitation several times since the end of the Franco era. The latest political controversy regarding Valencian occurred on the occasion of the drafting of the European Constitution in 2004. The Spanish government supplied the EU with translations of the text into Basque, Galician, Catalan, and Valencian, but the Catalan and Valencian versions were identical. While professing the unity of the Catalan language, the Spanish government claimed to be constitutionally bound to produce distinct Catalan and Valencian versions because the Statute of the Autonomous Land of Valencia refers to the language as Valencian. In practice, the Catalan, Valencian, and Balearic versions of the EU constitution are identical, although some compromises over spelling may have been involved in making them so.
Most current (21st century) Valencian speakers and writers use spelling conventions (Normes de Castelló, 1932) that allow for several diverse idiosyncrasies of Valencian, Balearic, North-Western Catalan, and Eastern Catalan.