The connections shown by these particular examples hold in general: given a transformation, you have a function and a relation; given a function, you have a relation and a transformation; given a relation, you have a transformation and a function: one thing — three aspects; and the fact is exceedingly interesting and weighty.
Mathematical Philosophy: A Study of Fate and Freedom, Lecture X (pp. 167-168), E.P. Dutton & Company. 1922