This is the passage in question:
When I sat with the philosophers I listened to them discuss very seriously a book called Process and Reality by Whitehead. They were using words in a funny way, and I couldn't quite understand what they were saying. Now I didn't want to interrupt them in their own conversation and keep asking them to explain something, and on the few occasions that I did, they'd try to explain it to me, but I still didn't get it.
Whitehead is a famous mathematician, so possibly Feynman felt he may have a chance of understanding what the philosophers were discussing.
Finally they invited me to come to their seminar.They had a seminar that was like a class. It had been meeting once a week to discuss a new chapter out of Process and Reality some guy would give a report on it and then there would be a discussion. I went to this seminar promising myself to keep my mouth shut, reminding myself that I didn't know anything about the subject, and I was going there just to watch.
Feynman admits to himself and the reader that he knew nothing about the subject.
What happened there was typical, so typical that it was unbelievable, but true. First of all, I sat there without saying anything, which is almost unbelievable, but also true. A student gave a report on the chapter to be studied that week. In it Whitehead kept using the words "essential object" in a particular technical way that presumably he had defined, but that I didn't understand. After some discussion as to what "essential object" meant, the professor leading the seminar said something meant to clarify things and drew something that looked like lightning bolts on the blackboard. "Mr. Feynman," he said, "would you say an electron is an 'essential object'?"
Feynman is completely lost in the discussion which is why he keeps quiet, "unbelievably" as he puts it. The professor seeing him keep so quiet takes pity and attempts to draw him into the conversation.
Well, now I was in trouble. I admitted that I hadn't read the book, so I had no idea of what Whitehead meant by the phrase; I had only come to watch. "But," I said, "I'll try to answer the professor's question if you will first answer a question from me, so I can have a better idea of what 'essential object' means. Is a brick an essential object?"
He's brave enough to admit he has not read the book, and perhaps taking umbrage, attempts to turn the question to his advantage - he has a certain strategy in mind, that is:
What I had intended to do was to find out whether they thought theoretical
constructs were essential objects. The electron is a theory that we use; it is so useful in understanding the way nature works that we can almost call it real. I wanted to make the idea of a theory clear by analogy. In the case of the brick, my next question was going to be, "What about the inside of the brick?" and I would then point out that no one has ever seen the inside of a brick. Every time you break the brick, you only see the surface. That the brick has an inside is a simple theory which helps us understand things better. The theory of electrons is analogous. So I began by asking, "Is a brick an essential object?"
Then the answers came out.
The positions that he has thought of in this passage have been discussed by philosophers, but he's not familiar with the technical terms by which they're discussed.
One man stood up and said, "A brick as an individual, specific brick. That is what Whitehead means by an essential object."
Another man said, "No, it isn't the individual brick that is an essential object; it's the general character that all bricks have in common, their 'brickness' that is the essential object."
Another guy got up and said, "No, it's not in the bricks themselves. 'Essential
object' means the idea in the mind that you get when you think of bricks."
Another guy got up, and another, and I tell you I have never heard such ingenious different ways of looking at a brick before. And, just like it should in all stories about philosophers, it ended up in complete chaos. In all their previous discussions they hadn't even asked themselves whether such a simple object as a brick, much less an electron, is an "essential object."
Feynman finishes his parable by claiming that they hadn't thought about what's meant when it's quite clear that they actually have (otherwise they couldn't have dreamt of such ingenious different explanations).
Feynman does this quite a bit in other fields he's not an expert in. That is, he plays fast & loose: At school he cobbles together an English literature essay in competition with a rival by examining how the teacher can be impressed - by using synonyms - not understanding that literature is a means of examining the human predicament amongst other things. At College he teases mathematicians by making fun of their constructions - the Banach-Tarski paradox in measure theory - not realising that though the fields intersect their concerns are different. He makes fun of social rituals until he begins to realise that there is a point to it (his first wife tortured him with his catch-phrase 'what do you care what other people think'). He almost does the same thing with art, but he manages to get an artist friend to actually teach him how it's done. He eventually discovers that he can begin to make some value judgements by looking at some art - which to him comes as a surprise.
This is why Freeman Dyson in his book Infinite in all Directions calls Feynman half genius & half clown. The point of this exposition is to show that Feynman is not the physicist to go to if you want to find out what philosophy is up to. Although you characterise your question as simple, it is clear that it is not. To discuss it already means to discuss the World (the universe):
A brick is a massy object (need to discuss gravitation), it's held together by electomagnetic forces; to talk about why the electrons circling the atoms just don't spiral in, you'll need to discuss (early) quantum theory. To have atoms of such high atomic number that you'll need to talk about the furnace at the heart of a star and supernovas. A brick is not any piece of rock, so you'll need to talk about its manufacturing and how humans came to develop the technology to make it, which also means to discuss the nature of social organisation and industrial process. Its place in architecture. Then: what is man that he has a mind that can make such things? And what is mind & what is matter? And why a brick - why any thing? Did a God create the universe to create a brick? Did he know that he did or did he not know that he did or didn't. What do we mean by know here? And why am I gendering God?
William Blake (poet/artist) puts all this much better:
A World in a grain of sand
Of course none of this discusses the brick's essential nature; I freely admit: like Feynman I know nothing about the meaning of this particular technical term and its many forms. But what is quite clear is that a brick is not, as you allege, a simple object. To answer this question properly - that is, what it is and additionally where it comes from - is not a question of Physics as it's understood today. Each time physics tries to get at the what and the where of it and resolves it to some extent - the subject moves a step further back. Physics relates things, and only inquires into what as much as it can be resolved into a question of relationships. Feynman endorses at least this view when he discusses energy (I forget which book). This question is fundamentally one of metaphysics (in Aristotles time this meant after physics).
Perhaps you can begin, as Feynman did not, by reading Whiteheads Process and Reality? But this is going at it backwards, it's probably best, as Alice was advised in Wonderland:
"Begin at the beginning,", the King said, very gravely, "and go on till you come to the end: then stop”