Equivalence across legal systems is not something comparative lawyers assume lightly, but rather is the result of analysis. When comparing legal concepts, the fact that two terms share a translation or appear to perform a similar function is relevant, but it is only the beginning of the inquiry.

Comparative analysis looks deeper at doctrinal structure, purpose, scope, institutional context, conditions of application and legal effect. Take good faith. The expression is recognisable across numerous legal systems, but recognition of the label does not establish that the underlying doctrines are identical.

In one jurisdiction, good faith may operate broadly across contractual interpretation and performance. Elsewhere its role may be narrower, with other doctrines performing functions that would be associated with good faith in another system. A comparative lawyer therefore needs to consider how the concepts actually relate. They may be closely equivalent, overlap in certain contexts or perform only some of the same functions.

This methodology has an obvious application to AI. Cross-border AI systems also need ways of connecting legal concepts, but if those connections are based predominantly on terminology or statistical similarity, superficial correspondence can become embedded as legal equivalence.

Comparative law provides a more disciplined basis for making these connections. Rather than requiring every relationship to be binary, concepts can be mapped according to degrees and dimensions of overlap, with differences preserved alongside similarities.

At TransLegal, this is central to how we approach structured comparative legal data. We are not trying to force the world's legal systems into a universal taxonomy, but to represent their relationships in enough detail that downstream AI applications can use them intelligently.

Comparative law does not remove the need for abstraction. It can, however, make the abstractions more informed by ensuring that decisions about equivalence are based on how legal concepts actually function rather than simply on the terminology used to describe them.