Sacca or Truth is the constant faithfulness or concordance of a mental or apparently physical phenomenon with that natural state devoid of cognitive stains.
It is of two kinds:
Conventional or relative truth.
Ultimate Truth.
CONVENTIONAL TRUTH is the truthfulness of the customary truth used by the great majority of people, such as "Self exists", "a living soul exists" "I exist", "there is individual existence" and so on.
The customary manner of speech of the great majority of people who have no intention whatever of deceiving others uses the illusions of Cognition and this is completely correct as long as they are not clinging and craving to any aspect of these traditional useful truths.
All these truths are illusion (though useful in daily life) which erroneously regards impermanent as permanent and non-self as self. So long as this erroneous view remains undestroyed, one can never escape from the traps of Acquisition, Confusion, Aversion and a clinging or craving to what may lie in the future.
ULTIMATE TRUTH is the absolute truthfulness of assertion or negative in full and complete accordance with what is actual -the elementary, fundamental qualities of phenomena.
However this Ultimate truth, the experiences of the elementary, fundamental qualities, is generated by the mind, so it also is Illusion.
So that which exists is illusion and that which does not exist is also illusion.
When stating a conventional truth in affirmative form, one may say:" "mind exists" "consciousness exists", "sensation, discrimination and perception exist", "material forms exist" and so on. Yet knowing at the same thime that these things in truth do not exist one can reduce the level of clinging and craving.
Yet the non-existence of any phenomenon is also a lie, for it generates a duality, existence and no-existence as a potential.
It is then correctly said that there is neither Self nor No-Self, etc.
This appears to be paradoxical, but it is not. It means that while there is the useful Samsaric illusion of an apparent self, that is all that it is. The illusion does not have a counterpart in duality, for it requires the cognitive mind to create it.
The idea central to this is directly related to Vipassana, which is essentially the revelation that all phenomena are generated by the mind -even mind itself.
What use does this have? It allows one to listen to the natural voice of the system with confidence and use the illusions as a valid tool. It is a grave error to permit the cognition ruled by identity to be the controller of all behaviour.
Vipassana's cleaning process then involves readjusting perceptual function, vigilating cognition for correctness and,, most importtant of all, cleaning up the stains of Identity traces in Memory.
But be aware of the significance of the introductory sutras.