  Episodic memories are further distinguished from semantic memories by the Previous Awareness Condition on episodic memory. The Previous Awareness Condition has been developed and examined by Sydney Shoemaker (1970), among  others. Put simply, one has an episodic memory of an event only if one was agent or witness to the event remembered. The Previous Awareness Condition is a necessary but insufficient condition on episodic memory. If one has an experience as of being lost in a store as a child, but one was not in fact lost in a store as a child, such an experience is not an episodic memory. On the other hand, each of us has been agent or witness to many events of which we have no episodic memory. For example, one may not remember one’s third birthday party and so lack an episodic memory of an event to which one was surely witness.