title: Why does Objective-C use YES/NO macro convention instead of true/false?
body: <p>Most languages use the <code>true/false</code> keywords for boolean values.  I found that even Smalltalk is using <code>true/false</code>.  I know Objective-C is just borrowing concepts from Smalltalk, not the language itself, but I'm curious why it's using <code>YES/NO</code> instead of the more widely-used <code>true/false</code>.  Is there any historical reason?</p>