[bombcar]

A doorknob tells you the door will open, but doesn't tell you which way it will open, so you have to add something (a signifier) to the door if you want that.

Whereas a pushbar both tells you the door will open and how to do it and it's all tied together without a sign.

[OJFord]

Yes, that's exactly how I understand affordance. I just didn't get the distinction between original & current meaning other commenter described.

[bombcar]

It sounds like someone described a real problem (ambiguous interactions with everyday things) and someone else stole that term and said "we can apply it to the thing we add to fix the problem we created with our bad design".

Sadly, this kind if linguistic trick is quite common.

[OJFord]

Well, with the distinction being made it seems that a door push plate with barbed wire welded to it would be a current/changed meaning affordance that it can't be pushed (or anti-affordance if you will) but in the original meaning.. it's either neutral or an affordance that it can be pushed because it physically can be.

Or a pull handle on a door that should actually push open - I think that was an example given when I studied it, I think there was another term for it but I can't recall, a 'misleading affordance', say. But in the supposed original meaning it's just still an affordance for pushing, because it does physically allow that, even if it looks like it should pull?

If it's correct, the original meaning just seems redundant to me, the changed one seems to make more sense and be more useful, but perhaps I still haven't understood the top level comment.