The definition treats usability as a relational property of product and context, not an inherent property of the product

What it is

Read by the standard's definition, usability does not belong to the product but to the relation "product–user–goal–context": change the product, the users, the goals, or the context, and usability changes with it. In the normative sense, "this product has usability" is not a well-formed claim; the well-formed claim is "under these conditions it exhibits this level of usability."

Why it happens

The signature of a relational property is that altering any member of the relation alters the value. Inherent product properties (weight, color gamut) do not change with the user; usability shifts with user capability, task structure, and context—which is exactly why the definition places it in the relation. This reading explains the wording choice: the definition's subject is "the extent to which a product can be used," not "the product is easy." Misreading usability as inherent produces two practical errors: labeling a product permanently from a single test, and dismissing the correct rebuttal "our users differ" as an excuse.

Studying it

The property is testable: measure one product across multiple user×task×context combinations; if scores vary significantly across combinations, the relational reading is confirmed. Transfer datasets of the same product across populations and settings are natural evidence. The methodological corollary: usability conclusions must declare their scope of conditions, meta-analyses must stratify by condition set, and pooling scores from different sets manufactures artifacts.

Where it stops holding

Relational does not mean incomparable: with conditions fixed, designs and versions compare fairly, and design genuinely contributes to usability across many condition sets—good design stays strong over a wider range, which is "robust usability." But robustness is itself a relational statement, not a product label. Industry shorthand ("a highly usable product") abbreviates a condition set; formal documents should expand it.

Applying it

• Upgrade document phrasing: replace "our product is highly usable" with "under [users×goals×context], it reaches [metric level]."
• In procurement and bid reviews, require vendors to report evidence by condition set; reject unconditional absolutes.
• Set the design goal as "widen the range of conditions where high usability holds," verified by multi-condition testing rather than a single passing setup.

Related

• Same group: B5.08.1 The standard definition confines usability to specified users, specified goals, and a specified context of use · B5.08.2 Context of use includes device, physical environment, and social environment—not just the interface · B5.08.4 Newer standards place usability inside a broader quality-in-use concept alongside accessibility, not containing it
• Nearby: B5.01 Usability Definition · Q4 Measurement and Reliability
• Search terms: relational property · usability attribution · robust usability