than its direct ancestor. According to scholar Koldo Ulibarri, evidence is so scarce that it is impossible to prove either theory.

The reconstructed stages of the Basque language are Common Basque (5th-6th centuries AD), the common language from which all historical Basque dialects diverged, and Proto-Basque (1st centuries BC), an earlier stage preceding contacts with Latin. Some scholars further divide Proto-Basque into sub-phases, such as Joseba Lakarra's