Definition of Rationale

Definition Last Updated 17-Dec-2015 12:51

A rationale is an argument for or against something, which may be engaging in an activity or being in a particular state; a rationale is therefore a kind of rule.

Rationales necessarily include valuations because to argue for or against something is to say that it is absolutely good or bad, or relatively better or worse than something else.

Rationales should be sound arguments, i.e. arguments that apply valid reasoning to true premises.


Rationale is a defined term of Enterprise Architecture. Rationale is a defined term of Business Analysis


Article Last Updated 17-Dec-2015 12:51

Note the emphasis on the above use of sound as a qualifier of argument: whereas a valid argument is an argument that reasons correctly from the premises to the conclusion, a sound argument is a valid argument whose premises are also accepted as true, thus the soundness of an argument depends on what the intended audience of the argument accepts as true premises (as well as valid reasoning).

Rationales are ubiquitous – everything is done for a reason, even if it is also true that some things happen for no reason other than the ineluctability of causality – but they are particularly prominent and important in requirements analysis, risk management, stakeholder analysis, policy development, etc. where traceability to axioms or assumptions is the only guarantee of internal consistency.

In providing a rationale for a requirement the nature of the stakeholders with an interest in that requirement must be taken into account in expressing the rationale; both the stakeholders’ motivations and the premises they accept or reject must be accounted for. Note that if the requirement is, ultimately, contrary to certain stakeholders’ expectations, the soundness of the rationale will be crucial to obtaining stakeholder approval for that requirement.

Rationale is often explained simply with respect to reasons; the use of the word motivation in the definition given here highlights the ultimate dependency on the value of something to somebody.

Sometimes it may be necessary to explicitly state the value by reference to something else of known value, and sometimes it may be sufficient to imply a relevant value.

For example, assume a requirement that a user’s email address must be obtained – the rationale might be that failure to provide an email address would preclude the completion of some business transaction such as a sale (explicit reference to business value), or that failure to provide an email address will cause a software error (implicit reference).

Rationales are essential components of requirements – and a single requirement may have several rationales; rationales may also be used to clarify the relationships between requirements.

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