508 HARVARD LAW REVIEW. other to accomplish. In the majority of acts, the intent and the efficient energy unite in the same individual ; but there is no insuperable obstacle to their separation. In fact, as civilization becomes more intricate, this sort of separation becomes more fre- quent; and as individual needs become more complex and less easy of satisfaction by the individual himself, action through others becomes more and more necessary, and the forms of such action become more and more complicated. The possibility of the existence of such relations between man and man is due to the possibility of communication, the means whereby men make known to each other their various thoughts. Whatever be the form which the relations resulting from such a separation of the preconceived idea from the subsequent act may take, it depends upon this communication of ideas. The thinker, after conceiving his purpose, must state it, and the actor must accept that purpose so stated as an end to be accomplished before he can act at all. The thought so expressed on the one hand, and so agreed to be followed on the other, is the very determining ele- ment of the relation. Indeed, the relation is exactly what this mutual understanding is, neither more nor less. In the ethical and juridical handling of it, the mutual understanding must there- fore be constantly regarded and as constantly held to be the norm of construction. One source of difficulty in practically dealing with this mutual understanding is due to the presence in it, oftentimes, of certain vague and undetermined quantities of custom. Usual exigencies call into being usual means for their satisfaction. The needs of commerce, for example, are the occasion for numerous forms of credit capable of transmission from hand to hand and place to place. These and the like involve within broad limits substan- tially identical relations. Thousands of dealings are had in which the only observable differences are those of names, dates, and amounts. Thus a certain routine character attaches to them, and they fall into well defined classes. Men assume, without overt expression and often without even mental advertence to the point, that these usual elements enter into their dealings, and transac- tions of such a character must be interpreted with reference to them. The nature of the question involved in their construction, how- ever, is not thereby changed. To determine the nature of a given relation of this character, we first ask. What was the mutual
