(What follows is metaphysics - it is neither proved nor disproven by 'evidence', because metaphysics is prior to evidence; evidence can only illustrate a metaphysical scheme.)
First (by an act of assumption) we divide our experience into percepts, which come into us via the senses - and from memory; and concepts.
Concepts are primary, because percepts can only be understood by means of concepts. (Incoming sensory 'data' is just random and meaningless noise - unless and until interpreted by concepts.)
In other words 'information' or (more clearly) 'knowledge' is only possible due to a pre-existing interpretative scheme into-which percepts are inserted. Mere sensory data - such as photons coming at the eyes, or vibrations coming at the ears, the the consequence nerve impulses... these mean nothing at all. All their meaning comes from the fact they are interpreted by out pre-existing concepts.
So concepts are primary - and if true knowledge is possible, then the validity of true knowledge must come from the validity of concepts.
(If true knowledge is not possible, - why are you reading this? Why are you even thinking? Our first assumption must be that true knowledge is possible or else there is no point in thinking about knowledge. That is not a proof of the truth of knowledge, it is another metaphysical assumption.)
So concepts must be valid - or at least some concepts must be valid. And if concepts are valid then for knowledge to be public and shared, then concepts must be public and shared.
It seems that when we use true concepts to understand the world, this means that each of us is thinking using the same concepts - I mean exactly the same concepts.
So concepts are not located privately in our brains or minds - and certainly concepts are not communicated via percepts (concepts are not shown, or heard, or explained) - true concepts exist in some place where everyone can access them and can think with them.
(As a metaphor, concepts are somewhat like a radio station, but a radio station not broadcasting from a particular antenna but located everywhere; with everyone always being permeated by radio waves, everyone potentially able (with the right equipment) to hear exactly the same radio programme; and any number of people may tune-into the signal if or when they want to hear the programme.)
The point is that it is concepts, not percepts - it is our ideas and not our sensory data - which confer validity to our knowledge, and enable knowledge to be shared - which enable true and valid communication.
Consequently, if we can think purely conceptually, then our thinking will be wholly valid.
Therefore pure conceptual thinking - thinking without any percepts at all, thinking without any evidence, would be intrinsically valid, intrinsically true.
True although also partial and imperfect, insofar as our ability to access use concepts is incomplete in various ways and to various extents - so we all access and use the same concepts but from different and incomplete points of view.
To reiterate - the above is metaphysics - that is, it is a basic framework for structuring our understanding of reality - including all forms of 'evidence' including science. Its possible value comes from providing a way we can understand the possibility of valid knowledge at all, and how we personally may have valid knowledge, and how we may share and communicate valid knowledge with other people.
And it points to the central role of human thinking in knowledge; because thinking is where we put-together percepts and concepts; or else work-with pure concepts. Indeed, thinking, by this scheme, has not just a central role; indeed pure conceptual thinking is the unique basis of our interaction-with - our participation-in - the rest of reality.
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Next, we need to know how we personally might engage in pure conceptual thinking, and know we were doing so. A topic for another post.)
(Note: the above is a re-explanation and re-interpretation of the argument of Rudolf Steiner's early philosophical book: The Philosophy of Freedom/ Freiheit.)
