Affordance
An affordance is something that helps the user get further with whatever they're trying to do: a button, a tool, a piece of documentation, another person on hand. Whether and how well something affords depends on what the user is currently pursuing. A screwdriver affords opening a paint can well, opening a stuck jar weakly, and driving a nail not at all; same screwdriver, different pursuits, different affordances.
Definition
A cluster of conditions external to the user that the user can integrate into their pursuit at a route-step to increase route efficacy.
Affordances are relational
The term names a relation between a user pursuing an intent and what's available to them at that moment. The relation is what "affordance" picks out — not any property of the object or surface in isolation. A Next button affords advancing through a wizard step for a user trying to do exactly that; presented to a user with a different pursuit, the same button affords nothing, and might register as noise, distraction, or a wrong route entry.
You can't evaluate an affordance without naming the pursuit it's being evaluated against. "This button is intuitive" or "this article is comprehensive" treats the character as inhering in the carrier, which slides analysis off the relation. Intuitive for whom, pursuing what? Without naming the pursuit, the evaluation isn't operationally meaningful.
Internal user-side capacities — stored mental procedure, body skill, attention, motivation — support pursuit but aren't affordances. The framework treats them as separate. Both matter for whether a step gets traversed; only the external is what design work shapes.
Fit-strength is graded
Whether something affords, and how well, is constituted by the encounter with the user's pursuit. The same conditions might fit one intent strongly, another weakly, and another not at all. Among candidates that fit, fit-strength varies — and that variation is what makes one affordance more or less route-efficacious than another.
A washer affords getting clothes clean. A washer-dryer fits the same pursuit more strongly. Both are route-efficacious; the second contributes more. Design work targets the gradient: every affordance the team builds wants to fit the user's pursuit more strongly than the alternatives the user could reach for — other provider affordances, third-party tools, user-external substitutes, or not-doing-it-at-all.
Affordances nest
A Next button affords advancing within the wizard step it sits in. That step affords completing its sub-transition within the wizard it sits in. The wizard affords completing the customization within the route opened by the lifecycle email. The email affords the discovery and entry that opened the route. Each scope's affordance is constituted by the user's pursuit at that scope, evaluating what fits.
"Affordance" without scope qualification means whatever scope the design or diagnostic question is operating at. Scope is named when a move depends on it.
Example
A user wants to add a teammate to their workspace. Several conditions could fit that pursuit. The Invite button in settings fits directly and strongly. The keyboard shortcut fits but weakly — undiscoverable for someone who doesn't know it exists. A help article on team management fits indirectly, opening a route into the invite flow rather than completing it. A Slack integration in the same workspace doesn't fit at all; it isn't a candidate for the invite pursuit, even though it's reachable from the same surface.
Change the pursuit to "see who's already in the workspace" and the evaluation runs again from scratch. The Invite button is no longer a candidate. The member list view, previously unmentioned, now fits strongly. Nothing about the buttons changed; the pursuit changed, and the affordances reconstitute around it.