On the Essence of Truth--The Essence of Truth
“The essence of truth reveals itself as freedom.” Freedom, we may recall, has an ek-sistent character--it stands outside itself by disclosing beings. Every comportment “flourishes in letting beings be” and is always going to be concerned in any particular instance with some particular being. But comportment itself goes beyond any particular being; it is “attuned” (Stimmung) to “beings as a whole.” It is from this more basic (or, for Heidegger, the most basic) attunement that any given disclosure of a being as a being occurs. As such, attunement can never be reduced to some “experience” or “feeling” as such particular (ontic) designations cover over attunement’s (ontological) essence. By reducing attunement to such things  attunement is understood in terms of something other than itself, which understanding can prevail only by sustaining this distorted understanding of attunement. This can easily be seen when we understand that any particular “experience” or “feeling” is possible only because man is essentially attuned to beings as a whole. What has been lost (or “forgotten,” as Heidegger will later put it) is our understanding of this attunement. This is because “[t]he openedness of being as a whole does not coincide with the sum of all immediately familiar beings.” In fact, it is often where beings are not familiar that our essential openness to beings as a whole “can prevail more essentially.” When we are dealing with everyday objects we do not question their being; their use is obvious and we see no reason to question or see the openness in which they appear as common objects (compare 116).
Precisely in the leveling and planning of this omniscience, this mere knowing, the openedness of beings gets flattened out into the apparent nothingness of what is no longer even a matter of indifference, but rather is simply forgotten.Freedom, as an attunement to beings as a whole that lets beings be what they are, “prevails throughout and anticipates all the open comportment that flourishes in it.” As the ontological/existential essence of the appearing of any particular being, freedom as openness enables the appearing of beings and continually sustains each appearing, thereby making correctness/accordance possible. The “as a whole,” as it is understood here, will seem to be “incalculable and incomprehensible” to our modern conceptions; we cannot understand it in terms of how beings are revealed today, for “[a]lthough [comportment] ceaselessly brings everything into definite accord, still it remains indefinite, indeterminable; it then coincides for the most part with what is most fleeting and most unconsidered.” While this is true, the indeterminable aspect of comportment as openness to beings as a whole cannot be reduced to “nothing” or some empty formality (as in a transcendental unity of apperception), but must be given a positive meaning (as with “letting be”): every comportment of a being is also “a concealing of beings as a whole.”
Precisely because letting be always lets beings be in a particular comportment  that relates to them and thus discloses them, it conceals beings as a whole. Letting-be is intrinsically at the same time a concealing.Every unconcealing of a being as something in particular conceals other ways that that being can be unconcealed. By doing so it conceals “beings as a whole,” or the open comportment that lets beings appear (see 127), forgetting the manner of its showing as presencing through unconcealment in preference to what is shown. By doing so man forgets the basis of every appearing and takes as self-evident a given mode of comportment and a particular way of appearing (see 115-116). As every unconcealing is a concealing, every aletheia is a lethe, untruth must be part of our analysis and cannot simply be ignored (see 119). We must, then, understand untruth positively as concealment/concealing.