You can describe a principle of the enterprise architecture, and assign it to most TOGAF definition types in the Governance tab.

Principles are specified during step 1 of the ADM, when you create the baseline description of the architecture.

Within the Description property of each Principle, specify what the principle is, what is its associated rationale, and what are its implications. This kind of information helps everyone understand and accept the principle itself, and enables you to use principles to explain and justify why certain decisions are made.