How do we know?
TRUTH is the correct perception of relations.  Our perception of relations is in a continual process of revision as new experiences add further information to our understanding. But how do we know the truth?  How can we be certain that our perceptions are correct?  The following editorial commentary has been added to help in this quest.                 
When CC Zain wrote the Brotherhood of Light lessons he never regarded them as something that should be blindly believed or taken purely on trust by his reader. He wished the student to develop their innate powers of reason and perception (ESP) so that each statement could be checked out and tested by personal experience.
To this end he wrote the NOT SOLD AWARD LESSONS which represent a complete course in Psychic Development.  These lessons are available to anyone who passes the final examination after each course.
Theses psychic senses, however, are not infallible. They are prone to personal bias, including distortion and misinterpretation, just as the more commonly accepted physical senses are.  To avoid this pitfall, they should be checked one against the other including both the astral and physical senses and they should be weighed in the scales of common sense and reason.
Arriving at the correct perception of relations, which is Truth, is an ongoing process. It was recognized by the ancient Greek Platonists. They used the Allegory of the Cave* to demonstrate how our
convictions about what truth is are based upon our cultural environment and those in the material and inner world that surround us. Until we can turn our attention to the inner world ourselves to see and reason about what truly is its reality, we may be subject to the same illusions as the allegorical cave dweller.
Truth is not something floating out in space somewhere, but rather something that can be had only though diligent effort in cleaning the lens of our own mind. It is achieved by removing the bias of emotional baggage that only distorts and filters our perceptions. This requires the use of Induced Emotion and Directed Thinking. The  Platonists called this process ‘The Dialectic’.  These distortions are the cultural conditioning process of religious, parental and societal influence. It is how we perceive what comes to us that creates the false images of ourselves and the way we see the world.
There is no easy road to correct knowledge. However, it is the Soul’s mission and destiny to possess the precious jewels of Wisdom and Love at the end of time.  Then and only then will it know the TRUTH that sets it free.
* From Book VII of Plato’s Republic  ‘Allegory of the Cave’