This page provides some concise guidance and commentary on claims, arguments and evidence.
|Identify the purpose of the CAE and the target audience.
|What decision is the CAE supporting? How is going to be used? What balance is needed between communication and reasoning?
|Check that the claim is a statement that could be true or false.
|Each claim should be a single statement only. Avoid the use of “and” or “or”. Use CAE Building Blocs to combine sub-claims.
|Identify any detailed context that is needed for the claims to be understood.
|The context (e.g. of the plant, operating modes, assumptions, environment) defines the scope of the claim. A claim may only hold true within the boundaries of that scope. Where context changes between claims make sure this recognised e.g. by making the environment explicit in the claim.
|Check the claim for overloaded, vague or ambiguous words (“safe”, “fault”, …).
|These may hide anything from further claims to assumptions that must be made clear. Some words have significantly different meanings in different contexts (i.e. overloaded) so special usage should be identified.
|It must be clear what system the claim refers to.
Check that the claim can be expressed as “ system (or object) X has property Y”.
|A claim should be clear and direct, focusing on one object or system and its property (e.g. reliability, robustness).
At the start of a case the X and Y may need redrafting to identify the system (or object) and property. Consider using concretion or substitution CAE Blocks.
|Ask why the claim might be valid. The “because” will identify the sub-claims that if true support the claim.
|What is your rationale for supporting a claim? How are you going to go about explaining why a claim holds true?
|Ask what is the general rule that provides the link between these sub-claims and the claim (this becomes the argument).
|The argument must provide a justification for the selected sub-claims and must explain how they support the claim.
|Identify the evidence artefact and the claim that is directly supported by the evidence.
|The evidence should be a “thing in the world”, e.g. a“test report”.
If necessary, develop further sub-claims and arguments to link this to the case.
|Explain whether the evidence can be trusted and why.
|How was it developed? What methods and techniques were used? Is it verifiable?
|Identify if the evidence is a primary source or has been derived from other reports.
|If the evidence is not direct it is more difficult to trust it. Consider additional justification for evidence trustworthiness.