If you did not have rules or specifications, you would not have norms, and the theory could not be normative. Most commonly the rules which establish the norms of rationality are taken to be those of logic. It is assumed that a person, or a rational agent, has a system of beliefs and a set of goals or desires or intentions. In that case, the norms of rationality require that the agent only make decisions which are in accord with its beliefs and its current perceptual inputs. It is allowed that the agent combine rules and beliefs according to the principles of deductive logic.
Some philosophers relax the requirements.
His idea is that the computational complexity of applying logic to a system of beliefs may be such as to make the problem of perfect rationality an intractable one. In order to allow for this, his theory of minimal rationality permits the use of heuristic solutions which can be expected not to be too far from giving a logically correct solution. In addition, many epistemologists consider induction to be be a rational, if fallible, means of acquiring new beliefs. What we shall mainly use is the fact that rationality is judged in terms of conformity to some set of rules or specifications. However, we would not normally be surprised at a decision or an idea that was arrived at by following a set of rules or specifications.