Todorov’s greatest contribution to literary theory was his defining of the Fantastic.
He defines the fantastic as being any event that happens in our world that seems to be supernatural.
Upon the occurrence of the event, we must decide if the event was an illusion or whether it is real and has actually taken place.
Upon choosing whether the event was real or imaginary;
The event that occurs is actually an illusion of some sort.
The “laws of reality” remain intact and also provide a rational explanation for the fantastic event.
He gives examples of dreams, drugs, illusions of the senses, madness, etc. as things that could explain a fantastic/supernatural event.
The supernatural event that occurs has actually taken place and therefore the “laws of reality” have to be changed to explain the event.
Only if the reader cannot opt for one or the other possibility is the text purely fantastic.