I believe you have to first lay a foundation for discussion. What is his definition of truth? It seems that he toggles between various views, from what you’ve provided.
Here are various subjective views:
*]Pragmatic: “truth is only what works”
*]Empiricist: “truth is only what we can sense”
*]Rationalist: “truth is only what can be proved by reason”
*]Oneness: “truth is only what is in harmony with all ideas”
*]Emotional: “truth is only what I feel”
[/list]In contrast to the above subjective views of truth, all of humanity throughout every age has commonly understood truth in the Aristotelian sense, which is “truth is only what corresponds to reality.”
You might also consider discussing a concrete example. For example, what would make this statement true: “The hat is red.”
We seek to answer the above question, not by what I feel or what you feel, or what I can sense or what you sense (e.g., I’m colorblind and my senses differ from others with regard to sensing color), or what I can understand or what you can understand (e.g. the science of optics, light reflection, wavelengths), etc.
All these things are important: what one feels, what one senses, what one understands, etc., but they do not DEFINE the truth. They only serve to help come to discover the truth.
My feelings cannot change the reality that surrounds me. Nor do my senses. Nor does my understanding. Consequently, they have no affect on the veracity of whether or not a hat is red.
In the example above, ask him if he should place his hand over his eyes, does he make the hat disappear? Is the hat not still there, reflecting light in some specific wavelength apart from what is sensed by only him?
Perhaps he mixes “belief” with “truth” as many I know do. A “belief” is “something that we hold true.” Truth is “that which corresponds to reality.” They are different words that mean different things and we shouldn’t linguistically confuse the two. Truth does not vary based upon my feelings, my ability to understand, sense, etc, because reality does not vary based upon these things. However, beliefs do vary because of these things. Yet, we may hold to a belief that is objectively true or false (depending upon whether or not it corresponds to reality).
We come to our beliefs in three ways…
- testimony of others
“The hat is red” is true (objectively speaking) only if it corresponds to reality. In other words, the only thing that would make the statement, “The hat is red,” true is if the hat were in reality, red.
As a colorblind person, I had to come to accept this understanding of truth early in life. When I see the hat as green, but everyone around me tells me it is red, then I have two conclusions I can draw:
- All the people I love in the world, the most trustworthy people I know who insist that the hat is red are lying to me, and I am right, despite the fact that they have no advantage in lying to me. The reality is that the light reflecting off that hat is in the wavelength of green, not red as everyone else has concluded.
- I need to trust the testimony of others and accept that what I see is not the truth. The hat is red. My senses don’t define reality, as my ability to sense things differs from others.
Which is more likely?
So why is it important that our beliefs are true? You might give him an example, such as the HEAVEN’S****GATE sect, who asserted a belief that their ‘god’ was on a spaceship in the tail of a comet, and if they committed suicide, they would join their god on the mothership. Tragically, they killed themselves. Now, if their beliefs are true, then they are on the mothership at this very moment. But if they are false, then they’ve made a tragic error in seeking a false happiness.
Humans are created to seek happiness. Truth is important because we may seek that which is only appearantly going to make us happy, but in truth will make us miserable. Thus, we fail in our quest for happiness by grasping for what is false instead of what is true.