The doctrine of Two Truths pertains to the difference between how things are perceived versus how they truly exist.

The first is referred to as conventional truth, while the second is referred to as ultimate truth.

The conventional includes concepts, labels, and distinctions that serve the purpose of aiding us in our navigation of the world. We perceive objects, events, places, and individuals as distinct entities with specific characteristics, which allows us to intelligibly interpret a vast sea of information.

The conventional is the realm of duality, which is just to say the variety of poles such as light & darkness, order & chaos, good & evil, life & death, or hot & cold. Conventional reality is, in essence, a play of many spectrums as phenomena always appear along one particular range or another and never in isolation. The various poles are merely the extreme ends of these various spectrums, and it is this to which the term duality really refers.

Conventional reality is characterized by conditioned existence. This is known by the term samsara, which means the cycle of birth, aging, sickness, death, and rebirth. It is from being trapped within samsara that beings experience duhkha, or suffering, which is the starting point of the Four Noble Truths.

Another distinguishing aspect of conventional reality is its transient and temporal nature. It is fundamentally impermanent and always in flux, with old forms constantly transforming into new forms in a seemingly ceaseless play of pure activity. The measurement of this transformation of forms is called time, and the experience of it is subjective in nature.

Conventional truth pertains to the relative understanding of the world. The word relative is used because everything within this sphere of reality is defined in relation to other things. One thing can never be defined in isolation from something else and always arises within a vast web of interdependent phenomena. This is the meaning of the phrase dependant origination and is the basis out of which the law of karma operates.

Overall, conventional reality encompasses the diverse array of worldly and mental phenomena, and conventional truth operates within the realm of language, concepts, and designations as distinguished by the discriminating mind. Therefore, conventional truth can be summed up as the perception of phenomena by the human mind.

What has been described so far is that which is encompassed by the term conventional truth. Next, the ultimate truth will be approached, but it must be borne in mind that this level of truth is beyond the ability of language to convey due to the fact that language is itself limited to the conventional.

Therefore, we arrive at the peculiar position of being forced to use the conventional to point towards the ultimate in the way that the finger points towards the moon. The key here is to avoid becoming fixated on the finger and to remember that the finger is itself representative of something beyond.

This brings us to the first key understanding regarding the ultimate truth, which is that of its ineffable nature.

This means that the ultimate is beyond conceptualization and can only be realized through direct experience. Intellectual understanding can never fully grasp the ultimate; at best, it can only serve the function of the finger pointing towards the moon of the ultimate.

The ultimate is beyond samsara. It is beyond all forms and temporality. The law of karma holds no jurisdiction within the realm of the ultimate as it undergoes no change or transformation and is beyond all causes and conditions.

For this reason, the ultimate truth is associated with Nirvana, the liberation from suffering, and represents the awakened mind.

The awakened mind, as opposed to the discriminating mind, is able to cut through the supposed distinctions of the conventional and arrive at the ultimate truth of shunyata.

What this means is that the ultimate truth encompasses the understanding that the interdependent nature of the conventional necessarily implies that all phenomena lack independent, inherent existence and do not actually exist as stand-alone entities despite appearing as if they are. This is the meaning of the concept of anatman or no-self.

A common example of no-self is that of the chariot. Which aspect of the chariot constitutes the essence of what would be considered "chariotness"?

Is it the wheels? The axel? The reigns? Quickly, we begin to see that the phenomena we label as chariot is in reality only a collection of aggregates with no clear or objective delineation of where it starts or stops becoming a chariot.

The ultimate truth recognizes that there is no permanent essence of "selfness" and that what we conventionally understand as the self is actually composed of combinations of material and immaterial processes, subject to change at every moment.

Shunyata is the nondual nature of ultimate reality. Ultimate truth transcends dualistic conceptions and distinctions, yet does not refute multiplicity or the play of forms within relative reality.

What it does is reject that the appearances within the conventional plane of multiplicity are themselves independent at the ultimate level. It is not about a denial of things themselves but that the identity of a chariot is ultimately a concept that is synthesized by our mind.

In this way, Buddhism reconciles duality with nonduality. The conventional truth is understood to be subsumed within the ultimate truth.

It is the same with the great Madhyamaka understanding of "Nirvana and Samsara are one." The conventional play of forms known as samsara is nondual with the ultimate realization of Nirvana. The separation between the two is ultimately illusory and the result of ignorance.

Thus, we see that the ultimate truth pertains to the deeper, absolute nature of reality beyond the surface level appearances and distinctions as generated by the discriminating mind. It is here where it becomes clear that the conventional is indeed the realm of perception, whereas the ultimate is direct realization of reality itself as experienced by the awakened mind.