Why is a genetic connection between Caucasian languages and Basque considered inconclusive?

Theories suggesting a genetic connection between Basque and the Caucasian languages are considered inconclusive because they lack sufficient evidence to establish a definitive relationship.1

In linguistics, a genetic relationship is established only when languages exhibit systematic matches in phonology, vocabulary, and grammar that can be traced to a common protolanguage, rather than resulting from chance or historical contact. While some scholars have noted shared features between Basque and Caucasian languages, these observations do not meet the rigorous criteria required to prove a common ancestry.231

Furthermore, even within the Caucasian language group itself, establishing internal genetic relationships remains complex; for instance, the interrelationships between North and South Caucasian families are currently considered uncertain due to the absence of regular sound correspondences. Consequently, proposed links between these groups and Basque remain speculative and lack the empirical support necessary for scientific consensus.1