Two Truths in Mahayana There are Two Truths in Mahayana Buddhism Conventional and Ultimate. I can't understand how it works. For example: Two Mahayana Buddhists have realized the absolute truth: and one Buddhist tells the other that he has a headache. But how does another Buddhist perceive it according to absolute truth?
The first thing to resolving your confusion is to understand what Madhyamakas mean when they start talking about &quot;absolute truth&quot; vs regular ordinary truth. And in these contexts Madhyamakas regard &quot;absolute truth&quot; as that which is arrived at when you go looking for the absolute i.e., when you start analyzing with logic and reason what is the absolute nature of things. It doesn't matter if the things you are looking for are persons, chariots, chairs, headaches, etc. If you take any of these things and then ask the questions, &quot;What is the absolute nature of these things? How do these things exist? How do they arise? How do they cease?&quot; and try to find answers by analyzing using logic and reason, whatever conclusion you come to about these questions after thorough analysis, that is what is regarded as the absolute truth. Absolute truth and Ultimate truth here refer to the same thing.
This is the procedure that Nagarjuna and Chandrakirti and the Madhyamaka sages layout in their famous treatises and commentaries. They begin with a thing and ask how does it arise? How does it come into being? How does it cease? And then the claim is made (using logic and reason) that if these things truly arise, then they must arise in one of four ways:

They could arise from self
They could arise from other
They could arise from self+other
They could arise from neither

Those four exhaust all the possible ways in which something could truly arise. Then they look at each of these four ways and ponder if any of them are sufficient and make logical sense. When analyzing thoroughly with logic and reason it is found that NONE of those four work out. They all lead to some logical fallacy, inconsistency, circular reasoning or absurdity. The result of looking for the absolute truth in how these things truly arise is nothing. They do not arise in any of those four ways, yet those four ways exhaust the ways in which things can truly arise. When you analyze thoroughly how things arise you come up empty.
It is this very fact, that you come up empty when trying to analyze how things truly exist with logic and reason, that is then labeled: &quot;the absolute truth.&quot;

Now, some people grow very upset with this. They look at the above and say, &quot;if that is true then nothing exists!&quot; which is nihilism. It simply isn't true that nothing exists. But that truth, that things exist, is a conventional one and not an absolute one. When you go looking for the absolute truth about how things exist you find nothing.

There is conventional truth. Which is not based on logic and
reason analyzing how things exist and trying to uncover the absolute
nature of things.
There is the absolute/ultimate truth. This is what you arrive at when using
logic and reason analyzing how things exist and trying to uncover
the absolute nature of things. And the result is empty. None of the
four ways in which things might truly exist can be found.

These are the two truths.
Let me know if this helps! If you wish I can provide references and citations from Sutra, Nagarjuna's treatise and the commentaries. Let me know if you want any of these things or if they would be helpful.

&quot;Two Mahayana Buddhists have realized the &quot;absolute truth: and one Buddhist tells the other that he has a headache. But how does another Buddhist perceive it according to absolute truth?&quot;
Now to apply the above to your question. According to the absolute truth when one of these Mahayana Buddhists, who has realized the absolute nature of things, perceives the headache they understand that that headache does not truly exist. They realize this because they have gone looking, again and again, for a truly existing headache using logic and reason and have come up empty again and again. They have analyzed it to exhaustion looking for a truly existent headache and can not find one. It exists merely by convention and being labeled. There is no truly existing headache that can be found. Which isn't to say the headache does not exist. It exists conventionally. That is all.