How do we know what we know?

[Angrboda]

This then begs the question: can we really know anything to be objectively true if everything we do passes through such imperfect filters as our senses?

It depends a lot on what you mean by knowing something to be objectively true. In a sense, science and empiricism are somewhat apophatic, a lot of it is concerned with determining what things are not as opposed to delineating specifically what things are (for example, Popper's rationalism, falsification, the null hypothesis and so on). What we typically refer to as objective knowledge rests on a number of assumptions, such as that the real world exists independent of our minds and that our senses and experience deliver valid information about the real world. It's impossible to know anything absolutely, and so our knowledge is framed within those assumptions. Within that frame, our senses, aided by methodological tools like science, we are able to produce models of reality which are useful and ostensibly true if our assumptions are true. Beyond that, I don't know what it would mean to have knowledge of objective reality.

You asked a followup question which, IIRC, was whether it was worth thinking about if the answer is no, that we can't have knowledge of objective reality. We don't actually have what classical philosophy would necessarily call knowledge of objective reality, but what we do have, given our assumptions, produces robust and reliable predictions about what we will experience if we do X or Y. That may not be absolute knowledge of objective reality, but since our experience is the only thing worth caring about, I hardly think the difference matters. Is it worth pondering the questions surrounding knowledge of objective reality? I think so, but then I'm somewhat biased as a philosopher with an interest in philosophy of science and epistemology. YMMV. But then, I only have to point to Karl Popper and Francis Bacon to vet my opinion on the value of thinking about such questions.

[Gwaithmir]

We can trust in the knowledge of that which withstands the scrutiny of empiricism.  Anything else would just be subjective conscientious fancy.

To be honest, knowledge must also be open ended and subject to revision in the light of new evidence.

[Foxaèr]

We can trust in the knowledge of that which withstands the scrutiny of empiricism.  Anything else would just be subjective conscientious fancy.

To be honest, knowledge must also be open ended and subject to revision in the light of new evidence.

Agreed. *bonks you from behind with my clothing constrained hard-on*

[bennyboy]

What can we confidently say is objectively true and true independent of the human experience? How much can we confidently say is true and how much are we assuming is true for the sake of our collective sanity?

Why do the figments of my imagination keep saying "we"?

[Aegon]

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objectively true
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Ugh!  Will no one rid me of this turbulent word?  

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What can we confidently say is objectively true and true independent of the human experience?
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"And"?  So what is the difference between a) objectively and b) independent of the human experience?  

True (or false) is a label applied to a proposition for a given epistemology.  It's relational, by definition.

I worded it poorly. Maybe I'm a wrong idiot, but to me a = b. The only way to say something is "objectively" true is when you can prove, to the best of your ability, that it is a valid statement even if humans weren't around to confirm its validity. Like.. the moon. Even if we were to argue that the moon doesn't exist unless somebody is observing it, we know from mathematical calculation that there's, at the very least, a massive object whose mass can impact the gravity here on Earth. So the moon, objectively, exists. That was my thought process. How many things can we say are objectively true by that criteria?

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How much can we confidently say is true and how much are we assuming is true for the sake of our collective sanity?

Think of all the social constructs we accept as normal unthinkingly (because they've been grandfathered) or rationally (because we recognise the social value)... 'money' being an obvious example of both.

I love deconstructing social constructs. I'm on board with you here!

You mean a process created by the human brain and performed by the human brain? It doesn't change the problem I outlined in the beginning of the OP

That's a problem between you and your brain, because my brain depends normally on empiricism.

Even then, an empiricist can accept one thing, and then 50 years when research develops and we realize that that one thing is false and a new thing is true, the empiricist was guilty of calling something a fact that wasn't. Not that I blame them, because I'd be in the same boat. If what we firmly think is true now is shown not to be in 50, 100, 150, etc. years... then that surely can't be objective knowledge or truth because we know it wasn't. So why call today's facts facts? 

That's the wonderful aspect of discernment between identifying as reasonable or religious.  Despite the facts that back up my current empiricist view, my mind can always be changed when the proper evidence is provided.  The same cannot be stated for those who are religious, for look how they attempt at altering science, intelligent design, in order to appease their biased religious views.

I suppose that's why we call very convincing scientific theories "Theories" regardless of the insane amount of evidence, but how many of us forget to be humble and assume what we think is true today is really, truly, objectively true?

Word salad.

But empiricism relies on your brain as much as the other way around! The point I was making at the end was: as an empiricist, would it be wrong to refer to what is true today as the truth, like you did in your first post in this thread? I mean... considering it may not be true in 50 years' time for the exact reason you're outlining. It's currently true, not OBJECTIVELY true. Do you see what direction I'm going with this? I'm trying to figure out how to best use the word truth and how to figure out how much I really KNOW vs how much is just a best guess. Most things are the latter, and if your conscious reality that you experience at all times, that you use to make all judgments, is also just your brain's best guess as to what is going on... on what authority do you claim to know what's true? We only know what's true in our own, human-brain-created realities, no?

But like Jorg said, which was a good way to put it: we make many assumptions based off our hallucinated reality every day and things basically respond the way we expect them to, so reality must at least be pretty close to what we see. It's still mind-blowing to me.

[Dr H]

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This then begs the question
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It doesn't.  It raises it.  

Thank you for that.