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So many basic discussions of affordances begin with the example of door knobs affording twisting. It seems to be the second example used in Norman's 1988 definition, even.

However a symmetric round non-knurled door knob gives absolutely no obvious clue for rotation or reason to explore rotating it, or even to push it. I think a door knob only affords a better grip for holding and pulling.

One explanation for why I feel this way could be because I grew up in India where I first saw similar tiny wooden 'knobs' used on old wooden cupboards, and these were simple lathe-turned wooden knobs with no rotating components. Doors typically had handles instead.

Is the twisting affordance attributed to doorknobs some other cultural phenomenon instead? If so what would one call it?


Edit: Some examples of door knobs being attributed turning/twisting affordances

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    The straight answer: They don't. That illustration is dumb. – plainclothes Apr 23 '15 at 2:22
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    Norman's example refers to a general knob such as a radio dial--not a door knob. Neither of the other references refer to a door knob. I think the question is flawed. We need to see an actual reference to assume your assumption is correct. – DA01 Apr 23 '15 at 3:42
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    I'm voting to close this question as off-topic because the premise of the question isn't backed up with citations that corroborate it. – DA01 Apr 23 '15 at 3:43
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    @tohster From Wikipedia: "For example, a knob affords twisting, and perhaps pushing ...". Some knobs do, door knobs typically do not except by social learning. – plainclothes Apr 23 '15 at 15:34
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    It seems pretty clear that multiple sources do say doorknobs have a turning/twisting affordance. slate.com/articles/technology/technology/2011/11/… books.google.co.in/… wiki.ubc.ca/Course:KIN366/ConceptLibrary/Affordances The question is why. One answer says because affordance has two common meanings... which makes sense to me. – Pranab Apr 23 '15 at 17:52
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“Affordance” is one of those terms that has come to be used for so many different things that I’ve recently just about given up using it in order to avoid confusion.

Affordance as possible physical interactions

In the original definition put forth by Donald Norman (1988) in The Design of Everyday Things:

The term affordance refers to the perceived and actual properties of a thing… that determine just how the thing could possibly be used (p9).

Note the use of the word “possibly.” Affordance is not a strong clue about the way you can interact with things. It all the ways it is physically possible to interact with things. So, by this definition, a doorknob does afford twisting with one hand. It also affords pushing, pulling, lifting, pressing, and slapping with the hand. It also affords licking with the tongue, kicking with the foot, and lifting with the knee. You can hang your hat on it. You can just look at it. There are typically many affordances for a given object.

Some of these interactions are part of the “correct” way to interact with the door knob/handle (twist and push/pull with the hand), some are not, but that’s okay. The affordances still rule out certain other ways you could interact with something. The doorknob doesn’t afford sitting –you butt physically won’t stay on it. It doesn’t afford swallowing –it won’t fit down your throat or even in your mouth. It doesn’t afford throwing (when screwed to the door). It doesn’t afford inserting your finger.

Affordance is a perceptual property developed through personal experience. For example, we learn at a very early age concepts like two objects cannot occupy the same space at once, and we learn to recognize hard stiff materials like metal, so that’s how we know, just by looking, that we can’t insert our finger in a door knob. However, affordance by this definition is pretty much culturally neutral: everyone everywhere learns pretty much the same things about the physical properties of shapes and materials.

So by this definition, door knobs and your door handles have the same affordances. Pretty much everything I said about door knobs applies to door handles. If you were to bring in a bunch of people who have never seen a door or cupboard before, they’d be equally likely to twist and pull both the door knob and door handle. Or hang their hats on them.

The lesson of affordances to designers is that, if you want users to interact with something in certain way, then make sure you give it a physical shape and structure with the right material to afford that interaction. It seems obvious, but there are certain cases where designers have failed by perceptually hiding clues of possible interactions.

Affordances as conventions

The term “affordances” took on a new meaning when it was applied to UIs presented on computer screens. By the old definition, every point on the computer screen has the same affordance. It doesn’t matter what it looks like or what it says –it’s physically possible to click, touch, lick, head butt, etc. any place on the screen. Affordances, by this old definition, is not a very useful concept to modern UI designers.

So a new much looser and less formal definition emerged, which is basically affordances are the interactions a thing communicates. Blue underlined text, for example “affords” clicking or tapping –more so than plain black text, or empty white space for that matter.

But what does that really mean? It means users have learned an arbitrary cultural convention –blue means "click this," black does not. This is the definition of affordance that you are using for door knobs versus door handles. By this definition, if a knob in you culture means pull, and a lever in your culture mean twists, then a door knob does not “afford “ twisting.

I’ve come to the conclusion that this definition of affordance is a disservice (even though I’ve used it myself). First of all it’s unnecessary. You can simply say “that’s the convention” or “that’s what users expect to do to that” or "that's a familiar idiom," or “that’s a consistent UI” (i.e., things that look the same as what the user saw before act the same as they did before). There’s no point in getting all jargony and saying “that’s the affordance.”

Second of all, I believe the new loose definition of affordance breeds in designers a misperception that certain visual properties on the screen inherently communicate interactions, the way physical objects inherent communicate possible physical interactions. With very few exceptions related to Gestalt principles, visual properties on the screen don’t have any inherent meaning. It’s all about what the particular user is used to. If we forget that, we can design the wrong thing for the wrong users.

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    Off the top of my head I think Don's door handle examples are more to do with whether its a push or pull door and how that's signalled by the handle design - and not these kinds of door handles. BTW - The original 1988 Basic Books edition is called "The Psychology of Everyday Things". – PhillipW Apr 23 '15 at 13:23
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    +1. For what it's worth, the term affordance was actually coined by James Gibson before it was popularized by Don Norman. This paper has an interesting discussion about the variances in definition, particular with respect to conveyance vs possibility. I will stand by my assessment of knob vs handle affordance and note that in Don Norman"s own house he has affixed green dots to his doorknobs to improve the affordance on which direction they turn. Handles don't have this problem. – tohster Apr 23 '15 at 13:47
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    That paper is a good summary: I've always found Gibson's view a bit metaphysical. Somewhere in POET Don points out that if you have to add a sign on an interface then its 'affordance' has failed ! – PhillipW Apr 23 '15 at 14:16
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    Excellent point on how blue text affords a 'click' for no reason other than we are conditioned to know that. I see a lot of physical UI discussions on here that argue how convention is no reason to continue a process, and yet that one slips right past! – Lee Harrison Apr 23 '15 at 14:26
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    Great response and summary – Tbolt Apr 23 '15 at 15:09
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As stated earlier, I think the title of your question is incorrect. Most citations referring to knobs offering an affordance of rotation are typically referring to knobs other than the ones on doors. Such as the ones on a radio tuner...which tend to have a lot more physical (and visual) cues as to how to interact with it (knurled 'grippy' edge, a tick mark to indicate position, a radius of labels around the perimeter, etc.).

A door knob, by itself, really doesn't offer any affordances that it can be twisted. It does offer the affordance of 'gripping' and that is something people use as an example of affordance. However, the act of twisting is more of a learned behavior (similar to the comment about underlined blue links in HTML).

A simple example in the real world that comes to my mind is my Honda's GPS controls. They consist of a dual-action knob that can act as both a joystick and as a dial. I don't find it intuitive, but figured it out finally via trial and error. When I had a friend in the car, I kept telling him to twist the knob to change menus and he couldn't figure it out. The catch was you had to hold a particular part of the knob to get it to twist. There was also no labeling or any other indication of what the knob did. You simply had to know ahead of time via training. My point being that knobs, by themselves, really do not offer up great affordance in terms of how to use them in a twisting motion. Knobs on devices tend to use a lot of secondary affordances to communicate 'twistability'. What makes door knobs 'twistable' has a lot more to do with history and learned behavior. As such, one could argue that any door knob today does offer affordability because we're already all familiar with other door knobs.

I would argue that saying 'door knobs offer good affordance as to being twistable' is simply a poor example of affordance. As to why people use that as an example, I'd argue that few actually do and that we misread 'knob' as referring specifically to 'door knob'. And those that do, many of them are referring to the affordability it offers up to be gripped--not twisted.

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They sometime don't afford twisting very well

Your observation is a good and nuanced one.

Door handles are used frequently as cases in design texts because they can represent:

  • A ubiquitous interface
  • A complex, compound interaction (the knob must be twisted in one or another direction, and then the door pulled, pushed, or slid)

Therefore, twistable door handles actually need to afford at least two motions:

  1. Twist the handle
  2. Pull/push/slide the door

Different door handle designs afford these motions differently:

enter image description here

....which is why lever-style door handles are common in many industrial or commercial buildings and are even mandated by some safety regulations around the world (California has even more strict regulations around public exits, requiring a different design of door handle altogether).

The round knob design persists today not because it has the best affordance, but for other factors which can supersede affordance including style (it's less intrusive, so you see it more commonly in home interiors), cost, mechanical durability, and symmetry (unlike the lever knob, round knobs can be indifferent to left/right handedness and left/right placement).

  • Lever based knobs are common because they mandated for ADA purposes (and have other benefits as well)--but not due to any sort of 'better affordance'. There's no need for a door knob to have any affordance in the modern world as it's a learned UI now. – DA01 Apr 23 '15 at 3:43
  • @DA01 once again we disagree. You would probably eradicate the example from design textbooks because it's "learned UI" but that cynicism destroys its intrinsic affordance, and also its didactic value. It's easy to pooh pooh good design just because it's commonplace. It's harder to appreciate its intrinsic worth which is something I hope textbooks continue to teach despite the views of jaded practitioners. – tohster Apr 23 '15 at 3:52
  • As I mentioned to the OP, I don't see any actual examples of a doorknob having an affordance to indicate twisting. I don't think it's actually used as an example much--namely because it's a bad example of affordance. Also, I'm not pooh poohing good or bad design or anything of the sort--but I do stand by my statement that a door knob doesn't need twisting affordance...it's a known feature learned by most humans for the past many hundreds of years. – DA01 Apr 23 '15 at 4:01
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    Though, I think it's important to point out familiarity can allow for affordability in other contexts. A lot of virtual UI affordability comes from mocking real-world objects. The affordability in that case actually may have more to do with having familiarity of the real-world object. – DA01 Apr 23 '15 at 15:17
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    @tohster "No amount of familiarity changes the fact that a kitchen knife affords cutting." This may be a whole new discussion > When would familiarity alter an inherent affordance? – plainclothes Apr 23 '15 at 15:38

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