If philosophy has to begin with reading those philosophers who came before then by definition philosophy could not have begun. Indian Buddhist philosophy regards perception and inference as the true two routes to knowledge. You have to experience and rationalize it for yourself to know that something is true. Secondhand information (knowledge) is firsthand knowledge of someone else’s knowledge.

There are things. I see them. I hear them. I smell them. I taste them. I touch them. I interact with it. I see you interact with it. I can draw the conclusion that it exists independently of me or you perceiving it. Sometimes I see it and you do not. And sometimes you see it and I do not. But they persist. And we assume that if neither of us see it, it still persists. If you can hold it, then I can hold it. Physical objects are real this way.

Without something called space we would not see individuated objects. Without time we would not see change in objects. We infer space and time this way. Reality is the totality of things, space and time.

Some people infer there is more. The things said to be unseen, unaffected, un-located are said to exist because they are thinkable. Even if they do exist by their own definition they do not interact with the things of reality. Again, by its own definition, ignoring it will have no consequences. For this reason it makes sense to be a materialist or physicalist.

Realists about matter, however, do need to explain how is it we come to “have” abstract entities. The answer is, as I have said, is that they are thinkable, or, to be precise, thought of. Let us be clear. Physical objects do not need to be thought of to exist, but abstract entities do. Furthermore, can it be truly said to exist simply because it is thought of?