'Act' or 'Actuality' traduces two words coined by Aristotle: energeia and entelecheia. The first meaning of energeia is movement (kinesis). The second meaning designs the end of movement: form, substance (ousia), essence. Here entelecheia is brought to design that final state in which things reach their end and perfection. The third meaning or application of ener-geia, and derivately of entelecheia, is operation, action, function (ergon).