[4][5][6] Gascon is mostly spoken in Gascony and Béarn (Béarnese dialect) in southwestern France (in parts of the following French départements: Pyrénées-Atlantiques, Hautes-Pyrénées, Landes, Gers, Gironde, Lot-et-Garonne, Haute-Garonne, and Ariège) and in the Val d'Aran of Catalonia.

Where a word originally began with [f] in Latin, such as festa 'party/feast', this sound was weakened to aspirated [h] and then, in some areas, lost altogether; according to the substrate theory, this is due to the Basque dialects' lack of an equivalent /f/ phoneme, causing Gascon hèsta [ˈhɛsto] or [ˈɛsto].

[8] Another phonological effect resulting from the Basque substrate may have been Gascon's reluctance to pronounce a /r/ at the beginning of words, resolved by means of a prothetical vowel.

[9]: 312 Although some linguists deny the plausibility of the Basque substrate theory, it is widely assumed that Basque, the "Circumpyrenean" language (as put by Basque linguist Alfonso Irigoyen and defended by Koldo Mitxelena, 1982), is the underlying language spreading around the Pyrenees onto the banks of the Garonne River, maybe as far east as the Mediterranean in Roman times (niska cited by Joan Coromines as the name of each nymph taking care of the Roman spa Arles de Tech in Roussillon, etc.).

[10][better source needed] A minor focus of influence was the Way of St James and the establishment of ethnic boroughs in several towns based on the privileges bestowed on the Francs by the Kingdom of Navarre from the 12th to the early 14th centuries, but the variant spoken and used in written records is mainly the Occitan of Toulouse.

[citation needed] The énonciatif (Occitan: enunciatiu) system of Gascon, a system that is more colloquial than characteristic of normative written Gascon and governs the use of certain preverbal particles (including the sometimes emphatic affirmative que, the occasionally mitigating or dubitative e, the exclamatory be, and the even more emphatic ja/ye, and the "polite" se) has also been attributed to the Basque substrate.

A poll conducted in Béarn in 1982 indicated that 51% of the population could speak Gascon, 70% understood it, and 85% expressed a favourable opinion regarding the protection of the language.

[15] However, use of the language has declined dramatically over recent years as a result of the Francization taking place during the last centuries, as Gascon is rarely transmitted to young generations any longer (outside of schools, such as the Calandretas).