D. CAUSA MATERIALJS The hypotheses of efficient causality were statements answering the question 'why' taken to mean, 'What is the stimulus-cause of emotion?' Hypotheses of material causality are statements answering the 'why' in another sense: 'What is the nature, the stuff of emotion?' The material cause, by dictionary definition (OED) is 'that of which something consists or out of which it is developed'. In order to group the hypotheses of this class of cause we must first get at the various criteria of matter that have been offered through the ages. A foremost distinction must be made at the outset: the concept of

matter,likethatofthematerialcause,isrelative.Itisnotanabsolute, eitherasameaninglessfictionofunrealityastheidealistswouldhaveit, orastheoneandonlyprincipleofrealityasthematerialistsmaintain.WeavoidbothextremesbyfollowingthecentrallineoftraditionbegunwithAristotle,usingtheconceptofmatterasco-ordinate withtheconceptofformandthematerialcauseasrelativetothe othercauses.