Obj C Code Help

[appleguru]

		SEL sel = @selector(lowercaseString);
		NSLog(@"Responds to Selector \"lowercaseString\": %@", ([myObject respondsToSelector:sel] ? @"YES" : @"NO"));
		if ([myObject respondsToSelector:sel]) {
			NSLog(@"lowercaseString is: %@", [myObject performSelector:sel withObject:self]);
		}

Why does that block of code report "self" as being undeclared? I thought you could always call something on self? If I change the self to myObject, it works fine. Any ideas?