Ephesians 2:2 

    (2) Wherein in time past ye walked according to the course ['aion'] of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience:



....Richard C. Trench is a resource virtually every commentator eventually quotes on the definitions of biblical words. He defines aion as:

    . . . all that floating mass of thought, opinions, maxims, speculations, hopes, impulses, aims and aspirations at any time current in the world, which is impossible to seize and accurately define, but which constitutes a most real and effective power, being our moral or immoral atmosphere which at every moment of our lives we inhale, again inevitably exhale.

Aion, translated as "course" in Ephesians 2:2, is the vague, ever-present immaterial realm that we are surrounded by and live in. It is interesting that Trench ties his definition to air, in that, even as we unconsciously breathe air in and out to sustain life, the course of the world is every bit as necessary to carnal life and is affecting us invisibly and constantly.

Second, Johann A. Bengel adds that aion is ". . . the subtle informing spirit of the Kosmos, or world of men who are living alienated and apart from God." This is what Germans termed zeitgeist, the spirit of the age—the "informing spirit"!

The term "spirit" is used to indicate the invisible, immaterial influence whose characteristics are absorbed and then manifested in the attitudes and conduct of the general population of a given people.