I doubt very much that you remember the day you were born. It follows that you cannot give me a description of exactly what you believed on that day.
At the present, you have a lot of beliefs that you don't even think about a bit but just presume are true.
A possible set of beliefs which might fall in that category:
1. You have eyes to see out of.
2. You can hear sounds.
3. You can feel things with your fingers.
4. You can taste different flavors.
5. You can smell things.
Those can be summarized as "you probably believe in the five senses".
Some more things you may also believe:
6. You live in a universe which (at least for practical purposes) can be seen as a three dimensional space occupied by "stuff".
7. You probably believe there is such a thing as "the past".
8. "the future"
9. "the present"
These are all concepts which you cannot prove to me that you believed the day you were born because you simply don't know what you believed then.
Suppose you go to great lengths to prove that babies believe all these concepts on the day of their birth and are actually successful in that proof. If you could do it you would only have moved the problem back to an earlier dilemma.
Then you would have to prove that the first appearance of life had the concept. Either that or you have to admit that the concepts arose in some way.
The fundamental issue is that our senses are part and parcel of our model of reality. Without the model, our senses are undefined!
Somehow "we" (we being either you and I, or humanity, or life, or -- whatever--) have managed to create a mental model of reality based on a totally undefined transformation of totally undefined information. And it works dammed well.
Since it has been done, we know it can be done. The question is how can it be done. If we cannot comprehend how that problem can be solved, how can we be sure that that the solution we believe in is correct? Oh sure, it works dammed well but that is not a proof that it is correct!
The problem is very simple. If you believe reality exists, it must be possible to create a model of reality given absolutely nothing but a collection of totally undefined data which came to you from reality via a totally undefined transformation process.
You know the problem is solvable because we have solved it (we have a mental model). I have found a solution to that problem. I do not claim my solution is the same solution provided to us by (???-- where ever it came from --??? call the original solver "God" if you want to: the issue is that the source of that solution has no impact on the existence of the problem at all). What I do have is a procedure for creating a model of "a totally undefined mass of information transformed by a totally undefined transformation" such that there exists no collection of information which can make the procedure (or the model so deduced) invalid.
It follows that, if you were to use my model, you could be assured there would be no errors in the concepts defined in that procedure. This puts one on extremely solid ground with regard to those concepts. That is, the concepts are well defined and known to be valid totally independent of the actual nature of reality. That puts us in a rational position to examine reality!
I have found a starting point, something no other philosopher has managed to put forward!
Does that make it any clearer? --- Dick
P.S. Consider the following thought problem!
You have died and gone to heaven. After a long time, you ask God how he created the universe. God offers to give a presentation of exactly how it is done but only if you agree to take a test when he is finished. -- You agree!
The problem is that God (being the extreme in every way) is a very boring speaker and you fall asleep as soon as he begins to talk. As you wake, he is explaining the test you are to take. God will create a universe of his own design and place you in that universe: i.e., you will be, in some way, aware of that universe. He guaranties that you will remember every thing you know but gives no guarantee whatsoever that anything you know will be applicable to that universe. In fact he tells you that he will do his very best to assure that as little as possible of what you know applies to that universe.
The test is for you to unravel the rules of the universe he has created.
Are there any concepts which you can confidently use to assist you in the investigation of that universe? That is, do you have any suggestions as to how you would prepare to attack the problem or would you just throw up your hands and leave the solution to your subconscious?