In practical terms, this is because use of the relation of causality is necessary for the interpretation of empirical experiments. Interpretation of experiments is needed to establish the physical and geometrical notions of time and space. Volition
The deterministic world-view holds that the history of the universe can be exhaustively represented as a progression of events following one after as cause and effect. The incompatibilist version of this holds that there is no such thing as "free will". Compatibilism, on the other hand, holds that determinism is compatible with, or even necessary for, free will. Necessary and sufficient causes
Causes may sometimes be distinguished into two types: necessary and sufficient. A third type of causation, which requires neither necessity nor sufficiency in and of itself, but which contributes to the effect, is called a "contributory cause". Necessary causes
If x is a necessary cause of y, then the presence of y necessarily implies the prior occurrence of x. The presence of x, however, does not imply that y will occur. Sufficient causes
If x is a sufficient cause of y, then the presence of x necessarily implies the subsequent occurrence of y. However, another cause z may alternatively cause y. Thus the presence of y does not imply the prior occurrence of x.
Contributory causes
For some specific effect, in a singular case, a factor that is a contributory cause is one among several co-occurrent causes. It is implicit that all of them are contributory.
Type 3, however, can be uniquely identified, since 
  
    
      
        X
      
    
    {\displaystyle X}
   and 
  
    
      
        Z
      
    
    {\displaystyle Z}
   are marginally independent and all other pairs are dependent. Thus, while the skeletons (the graphs stripped of arrows) of these three triplets are identical, the directionality of the arrows is partially identifiable. The same distinction applies when 
  
    
      
        X
      
    
    {\displaystyle X}
   and 
  
    
      
        Z
      
    
    {\displaystyle Z}
   have common ancestors, except that one must first condition on those ancestors.