Affordances are Inconceivable

tl;dr: "Affordance" and "signifier" sow confusion. Say "enabler" and "clue" instead.

Don Norman popularized "affordance" in The Design of Everyday Things. He borrowed it from James J. Gibson's wonderful work in ecological psychology, but the colloquial meaning has diverged from the original definition:

The design community loved the concept and affordances soon propagated into the instruction and writing about design. I soon found mention of the term everywhere. Alas, the term became used in ways that had nothing to do with the original.

-- Don Norman, The Design of Everyday Things (revised edition, 2013)

To most, an "affordance" is something that invites interaction. Even designers say "logout affordance" when they mean "logout button".

Norman rejected this use of the word:

No, that is not an affordance. That is a way of communicating where the touch should be. You are communicating where to do the touching: the affordance of touching exists on the entire screen: you are trying to signify where the touch should take place. That's not the same thing as saying what action is possible.

Here is Norman's original definition:

The term affordance refers to the relationship between a physical object and a person. An affordance is a relationship between the properties of an object and the capabilities of the agent that determine just how the object could possibly be used. A chair affords ('is for') support and, therefore, affords sitting. Most chairs can also be carried by a single person (they afford lifting), but some can only be lifted by a strong person or by a team of people. If young or relatively weak people cannot lift a chair, then for these people, the chair does not have that affordance, it does not afford lifting.

-- Don Norman, Design of Everyday Things

In other words, affordances are freedoms available to agents.

But a button's appearance may not match what it affords. Invisible logout buttons may afford logout; visible logout buttons may not afford logout.

Not only did my explanation fail to satisfy the design community, but I myself was unhappy. Eventually I gave up: designers needed a word to describe what they were doing, so they chose affordance. What alternative did they have?

-- Don Norman, The Design of Everyday Things (revised edition, 2013)

Norman solved this dilemma by coining "signifiers". Affordances describe what is possible; signifiers communicate potential action.

Now we have two incompatible meanings of "affordance". Purists prefer the original definition, while everybody else uses the colloquial definition.

It's time to deprecate "affordances" and "signifiers". Say "enablers" and "clues" instead:

Caution: when describing people, "enablers" and "disablers" are pejorative terms.

People already understand these words; they work without lectures on ecological psychology and design theory.

Claude Shannon didn't invent the word "information" -- he plucked it from a dictionary.

"Affordance" is an anti-clue -- it signals meaning it cannot deliver. Definitions only work when everybody shares similar understanding (or agrees that mutual understanding is tenuous).

Will "enabler" and "clue" catch on? Probably not. But at least they mean what they say.