Indeed, proof that a given condition always precedes or accompanies a phenomenon does not warrant concluding with certainty that a given condition is the immediate cause of that phenomenon. It must still be established that when this condition is removed, the phenomenon will no longer appear.

Claude Bernard (1813-1878) French physiologist, scientist

An Introduction to the Study of Experimental Medicine [Introduction à l’Étude de la Médecine Expérimentale] (1865)