Although a number of European Union legal documents require AI to be transparent, this is frequently not the case. Such opacity can be attributed to a diverse range of causes, ranging from so called ‘black box’ algorithms, trade secrets and patents, to the cognitive barriers of non-professionals. Transparency, in contrast, is, in many cases, indispensable for establishing generic or specific causation in deciding civil law cases, especially within the scope of contractual or tort liability. Therefore, the concept of causation applied in various parts of civil law should be rethought, and some remedies for this problem should be adopted.