Well, the tree seems to be there every day. I leave my window and come back. Yep, the tree is still in the same spot. There is, at least, a certain consistency to my observations over time.
And my wife sees the tree, too. In fact, every person that I’ve asked, sees the tree. So, there is, also, some shared perception (assuming I’m not imagining all the people who have told me they see the tree).
I can also do some experiments. I punch the tree. Yep, my hand hurts. Either the tree really exists, or I’m making it all up, in my mind — that the tree exists, other people see the tree, my hand hurts. And then there are the birds sitting in the tree. And the squirrels running up and down the trunk. And the fungus growing on the trunk, the leaves shaking in the wind, falling to the ground in the fall, etc., etc., etc.
I could be making all this up, but it seems a bit complicated (and getting more complicated the more I think of all the observations that interact with the tree’s existence). I am reminded of the days when people thought the Earth was at the center of the universe, and am struck by how my belief that “the tree only exists in my mind” becomes a similar argument; my imagination is the creator of the entire universe — the universe revolves around me.
Did I just hear the sound of a tree falling in a forest, and there was nobody around to hear it?
Well, I called this article, “Is truth a state or a process?” And if that tree exists, beyond my existence, then that tree exists whether I acknowledge it or not. This would argue that truth is a state, a state of reality, independent of my existence. However, my experience of the tree, interacting with it, observing it over time, communicating with others about the tree, experimenting with the tree, is a process.
Perhaps that which I believe is “true”, is an approximation to THE Truth. The Truth, though a state of the universe, is, for me, always a process. Even if I believe the tree exists, this is only an approximation to the Truth. My understanding of the tree’s existence does not (cannot) include all the meaning and understanding of the universal Truth about the tree’s existence. Another way of thinking of this is that the information content of the tree is interconnected with the information content of the entire universe, which is beyond my comprehension and beyond my capacity to understand. I can, however, get within “epsilon” of the Truth, if I’m willing, and able, to find new ways to test and observe the tree.
For me, it’s good enough that my hand hurts. I’ll accept that the tree exists. And for most of the things I want to do in my life, being within epsilon of the Truth is close enough. More importantly, if I want to get closer to the Truth, I’m going to need to listen to others, do some experiments, and keep my ears, eyes, mind, open. And even more importantly, I will only get closer to the Truth if I am open to information that I did not know. [And so, a corollary: The process of approximating the Truth involves a journey littered with beliefs that were not true. Learning is the process of correcting/changing/overturning previously held beliefs.]
I look out my window, and the tree is still there. The difference is that my hand hurts, and I learned a bit more about the Truth.
Note: My fascination with the process of truth began back in college, where I studied statistics and read de Finetti’s Theory of probability. For more resources on subjective probability, see Fishburn’s survey.
These days, I search for ways to use the power of computing to automate the search for Truth.
 Theory of probability, Volume I, Bruno de Finetti, John Wiley & Sons, New York, 1974.
 Fishburn, Peter C. “The Axioms of Subjective Probability.” Statistical Science, vol. 1, no. 3, 1986, pp. 335–345. JSTOR, www.jstor.org/stable/2245466. Accessed 10 Apr. 2021.