1. Information from Your Experience
There is a philosophical concept called naive realism which basically works under the assumption that the our perception perfectly represents the world as it truly is. This was an acceptable view for most of human existence, but science has shown us that subjective experience doesn’t match one to one with reality. We construct our perception of things based on senses that evolved to ascertain useful aspects of reality. What you see and hear is very different from what a snake or whale sees and hears. It’s even different from what I see and hear, albeit to a lesser degree. Paired with an incomplete input of reality is the imperfect way we recall it. Memories are reconstructed not replayed. Each recalling alters the events which will remain altered until the next time we recall them which alters them further. It’s the mental telephone game of our past. For these reasons, anecdotal evidence has little place in the lab and eye-witness testimony has lost much of it’s value in the courtroom.
2. Information from Consensus Experience
I put on a pair of black pants only to find my wife pointing out that they don’t match my shirt--because they are actually navy pants. Here we have two differing subjective perceptions and the only practical way to resolve who’s sensitivity to color is more correct is by crowd sourcing the rest of the family. When my kids, siblings and in-laws all tell me that my pants are navy, I have to admit that, regardless of my perception, the consensus is that my pants are navy.
Don’t worry, the majority of the time, your perception will be in line the perceptions of the consensus, but knowing how others observe things is still a big step in knowing that your observations are valid...especially if you’re a user of psychedelic drugs.
3. Scientifically Derived/Methodological Information
The entire point of the Scientific Method is to get as close to objectivity as possible in discovering what is true. Observations are still done with the subjective lens of the scientist’s senses, sure, but so are they recorded by machines. Data is computed and results are quantified to the most objective language, math. The biases of the researcher are overcome with placebos, controls and double blind studies. Finally, everything is peer reviewed and replicated independently. I consider this information as close as we can get to truth. That said, while there is no pragmatic reason to doubt it, I still recognize that it could be an illusion.
4. Philosophical Truth
Everything could be a lie covering the deeper truth of reality. I could be a brain in a vat and the inputs I believe I’m receiving could be electrical signals representing the whims of a mad man. I could be jacked into the virtual world of the Matrix. I could be telepathically manipulated by a trickster god. The only way to discover if there is transcendent truth beyond what I can perceive is, by definition, beyond my ability to perceive it. That is to say, there is the way. I find such a deception unlikely and at odds with notions like Occam's Razor, but the possibility is undeniable. Philosophical truth is a hypothetical that we may or may not be able to achieve, but even if we do achieve it--we won't know for sure that we have. Pragmatically we operate and reason using the axiom that reality as we understand it is, in fact, real.
What the religious often do.
The religious take philosophical truth, or Truth with a capital “T”, and believe that it is accessible via the deity they believe exists. They then elevate their belief that God exists to the level of Truth, which results in circular reasoning. Because I know God, I have Truth/I know God, because I have Truth. Outside of this circularity, the religious only have the least compelling class of information (1), to back up their claim of possessing the most compelling (4). Consensus and scientific information both trump what they label “Truth” which is a confusing and sometimes dangerous error of the mind.