Sentence:  Dreams that display events of the future with photographic detail call for a theory explaining their basic mystery and all its components , including that weird feeling of deja vu , inevitably fantastic though that <WSD>theory</WSD> must seem . 
Meaning of the word marked with <WSD> tags:  a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena