Material efficiency is a notion from Aristotle.

The material cause of x is the substance of which it is composed. Without the presence of that substance, x would not exist.

The efficient cause of x is the chain of events that have led to x's materializing. Efficient causation is how things in general come to be.

Material efficiency is thus the principle of physical reality. Conversation, on my theory, is a species of physical reality, from the syllables pronounced and issued on the wave forms of speech, to the thoughts in the bodies and brains of those present, to the cosmic impulse to speak and to express one's deepest need for recognition, for truth and for spirit vision.