Let’s start with the modest metaphysical assumption that we all live on planet Earth. This means we have a shared reality. One that is populated with various and sundry objects (or better, containing stuff that can be divided in to objects in any number of ways). This is the realm of objects, or the objective world. As embodied creatures, we are among the objects populating the objective realm. But in addition to being objects we are also subjects. As subjects, we have some limited experience of the world. Our experience is the one thing we are directly aware of, so no additional assumptions are invoked here. But there is one further small metaphysical leap of faith in presuming that we have experience of our shared reality. We could all live on planet Earth and yet be irrevocably plugged in to virtual reality machines, lacking any experience of the reality we share. But let us take that additional leap as well and assume that we have limited and fallible experience of a shared reality. Absent this step, we can not hope to communicate, understand each other, or interact at all.
As subjects, our experience of the world is limited by our perspectives. Further our impressions and beliefs are liable to be distorted by biases and other intellectual bad habits. So, one thing we can all recognize about being subjects is that our impressions, beliefs and opinions are fallible. We are limited and imperfect in ways that make error quite possible. That’s just life as a subject, having subjective impressions and beliefs means being fallible. Fortunately, we can always expand the basis of evidence we reason from by sharing our impressions and beliefs with each other. And we can improve the reliability of our reasoning by cultivating the intellectual habits that steer us away from biased and distorted beliefs. This is the point of critical thinking.
To say our impressions and beliefs are subjective is not to say they are always biased, distorted or false. Belief is always in the subjective realm because beliefs belong to subjects. And this is all it means to say that belief is subjective. But our beliefs are representations of our shared reality and it remains possible for many of our beliefs to accurately reflect what is going on in the world of objects. That is, our subjective beliefs can be objectively true. All it is for a belief to be true is for it to represent some aspect of the objective world the way it is.
Note that we as subjects are part of the objective world. So, my beliefs about your beliefs are beliefs about an aspect of the objective world and they can be true or false, accurate or inaccurate. No subject can ever completely understand another simply because the nature of being a subject doesn’t allow for one person to fully occupy the mind of another. But we can share quite a bit of our subjectivity through human communication, at least if we are clear in our expression and charitable in our listening.
As subjects, it is generally good for us to have true beliefs and avoid false beliefs. When we have true beliefs, we are more capable of acting effectively, achieving goals, avoiding hazards, and generally having a good time. I suppose this is a value statement, but not the sort of value statements anyone is likely to dispute. This much of the value of having true beliefs comes along with being subjects who have needs and goals in a world full of objects (and subjects) than can be helpful or harmful to us. So, special cases aside, it’s good to have true beliefs.
For your beliefs to be rational, or reasonable, is just for them to be held on the basis of the best reasons. Good reasons are reasons that that are truth oriented. This much is just definitional. All it means for your belief to be rational or reasonable is for it to be oriented towards truth, or held for the most truth-oriented reasons. This much should make it clear why it is good to be rational. Being rational is more likely to get you true beliefs and true beliefs are good because they help you act effectively, achieve your goals, avoid hazards and such. To be reasonable, in the literal sense of the word, is to be amenable to reason. That is, the reasonable person is the person who forms or revises beliefs by yielding to the best reasons. To be a rational believer is pretty much the same thing.
[It’s worth noting that the words “rational” and “reasonable” can also refer to choosing or acting in ways that maximize your values and interests generally, not just towards true belief. Words are often ambiguous. The way to be comfortable with ambiguity is to get clear on how words are being used and track the various usages. Talk of rational or reasonable belief can reliably be understood as truth oriented simply because to believe something is to take it to be true].
Rationality is not a kind of human imposed authority over what is true or what we should believe. Rationality does not dictate such things. The only thing that is authoritative concerning what we should believe is how things are in our shared reality. To believe something is to take it to be true. To believe rationally is just to believe in a way that targets the truth well. To believe irrationally is a way of missing the target of belief. Rational belief isn’t guaranteed to hit the target of truth. But irrational belief involves a kind of unforced error.
What is true doesn’t belong to anyone. No subject gets to dictate or decide what is objectively the case, except in the very limited respect where a person decides what to do, how to understand things, and who to be. As a subject, I have this much power over our shared reality and no more. So there is no “my truth” or “your truth.” There is just the truth, which includes what we do, how we understand things, who we are, our willingness or reluctance to appreciate the truth, and whatever consequences follow from this.
We’ve made two assumptions here. Namely that we have a shared reality and that we each have limited and fallible experience of that reality. To this we’ve added a few definitional remarks about truth, rationality, reason, belief, subjectivity and objectivity. And we’ve reasoned a bit on the basis of these things. In the definitional remarks I’ve tried to lay out standard philosophical usage clearly and straightforwardly.
Confusions about truth, rationality, subjectivity and objectivity abound in our culture at the moment. Many will be tempted to object to what I’ve laid out here on the grounds that people are free to define these notions as they please. In a sense, people are free to do so. Nobody has the power to prevent it. But to insist on defining things as we like amounts to the privatization and commodification of language, with the primary result of undermining our capacity to communicate with one another and understand each other in the limited ways that are open to us. I am no fan of such hyper-individualism. We already have capitalism run amuck even without such linguistic intellectual property. While we could quibble about how to define truth and rationality, the only result of this would be to talk about something else instead. Something other than how we stand as subjects to each other and our shared reality.
The reason it is good to understand truth, rationality etc. in the manner I’ve laid out here is that it facilitates clearer communication and understanding of our diverse experiences and diverse ways of thinking. This allows us to cooperatively improve our ways of thinking and our limited grasp of the truth. And as a result of this, we are empowered to act more effectively, avoid hazards in our interactions, and appreciate each other more significantly.