As a human, you have a remarkable capacity, quite unique among the animal kingdom as far as we are aware. What you can do is explicitly self-reflect and provide interpretations for your actions. You can also evaluate the accounts others offer and decide if the reasons they give for their behavior are legitimate.
What is this remarkable ability and where does it come from? Perhaps the easiest way to characterize this aspect of your self is to think about it as your ego. Your ego is the storytelling part of your conscious life. It narrates what is happening and why. It is a secondary stream of thought that monitors your primary experiential way of being in the world.
For most people (although not all), the storytelling self provides a fairly constant stream of chatter, an inner commentary and dialogue that attempts to develop a meaningful narrative about what is happening and why. Whenever your embodied, perceptual way of being in the world—let’s call that your “experiential self”—encounters something unusual or that requires deliberative thought to make sense out of, your narrator kicks in and starts with reflective and usual verbal sense-making to try to sort things out and provide a justification for what is and what ought to be.
What is this interpretive and reason-giving system and where did it come from? According to the Unified Framework, humans have a “mental organ of justification” that emerged in our evolutionary history because of language. Human language is remarkable in that it allows for a much more direct “intersubjective” highway to be opened up between minds. Consider, for example, my experience of redness. That private experience is hard to share directly. It is “contained” with my subjectivity. This containment is what makes it so hard to know exactly what it is like to be another sentient animal. Thomas Nagel famously made this point, asking, "What is it like to be a bat?"
Although I cannot share my subjective experience of redness directly with you, I can directly share with you my verbal thoughts about redness. For example, I can claim that, for humans, redness is associated with energy, anger, and passion because of its association with blood and sexual organs. Notice that this proposition has the same form, whether I say it privately or publicly out loud. This illustrates the crucial point that language-based thought moves between the private subjective and public intersubjective worlds with ease.
As anyone who has had a secret revealed to others can attest, we don’t always want our private thoughts to be shared publicly. This means that although the communication between subjective minds that was afforded by language was a tremendous advantage, it also was the case that our ancestors faced a new, complicated, and important problem. Specifically, what and how should we share with others? Put even more broadly, how do we justify ourselves to others? And how do we evaluate the justifiability of the accounts of others?
This is called “the problem of social justification.” The Unified Framework posits that as language evolved into a full question and answer system of communication, this would have been a new and crucial adaptive problem in the social world. Nature’s solution was the human ego—a storytelling “I” that narrates to others what is going on and why and does so in a way that takes the social context into account.
It is this verbal interpretative, meaning-making and reason-giving capacity that launches human culture and the Person-Culture plane of existence. So, what is the mental organ of justification? It is at the center of what it means to be a person. It is the narrator you call “I”.