一、苹果官方API的解释是：

isKindOfClass：Returns a Boolean value that indicates whether the receiver is an instance of given class or an instance of any class that inherits from that class.

isMemberOfClass：Returns a Boolean value that indicates whether the receiver is an instance of a given class.

isSubclassOfClass：Returns a Boolean value that indicates whether the receiving class is a subclass of, or identical to, a given class.

二、它们的作用的区别：

isKindOfClass：判断对象是否为某类或者其派生类的实例（对象方法）；

isSubclassOfClass：判断对象是否为某类或者其派生类的实例（类方法）；

isMemberOfClass：判断对象是否为某个特定类的实例（对象方法）；