1. I am not familiar with academic English, so some terminology might be imprecise. The goal is simply to convey the general meaning.

2. The following discussion includes some theological and religious ideas. Since knowledge was closely tied to the Church in the Middle Ages, and science was considered part of theology, these topics are hard to avoid. If that bothers you, feel free to skip this guide.

3. Most theories I mention are limited by their historical context and serve merely as a reference for the development of a chain of reasoning. Modern and contemporary philosophy often have deeper reflections on these theories. You are welcome to try and critique them yourself :)

Firstly, how do human beings recognize and transmit knowledge/experience? Humans typically observe things and use language to describe them.

This process of describing assumes that the natural world is intrinsically ordered. Otherwise, knowledge/experience could not be understood and preserved. If the world were complete chaos, we could not make sense of experiences or share them with others.

Therefore, this describing process is, in effect, also a process of classification or grouping(induction and summarization).

And this classification process, in turn, illustrates a key point: Knowledge, in the general sense, does not directly describe Thing A, but rather describes Thing A's position within a symbolic network — of which language is a central part.

With this basic viewpoint, let's now look at how people have understood the relationship between word and thing from ancient times to the present.

In early history, people were surrounded by mysteries they could not explain, unable to provide a rational explanation for many things. They began to seek a deeper and more fundamental kind of knowledge (let’s call it knowledge B)—a knowledge that could serve as the cause or foundation of everything in the world.

Later, Scholastic philosophy identified this knowledge B as divine knowledge, the knowledge of God.(for proof, see Thomas Aquinas's Five Ways of demonstrating God's existence). According to this view, such divine knowledge is revealed in the Bible.

Therefore, how the Church Fathers tried to reconcile the apparent contradictions between nature and Scripture will be our next focus. After all, many events described in the Bible do not seem possible within the natural order we observe.

Augustine offered an explanation. He argued that the multiplicity of meaning does not come from the word itself, but from the thing it names. Therefore, if you cannot understand the Bible, it's not because you misunderstand the words in the Bible, but because you don't understand the meaning symbolized by the things those word refer to. The thing itself, as a sign, points to other things. For example, a "fox" points to a "cunning person".

This kind of "pointer" (borrowing a term from programming) is by no means something we imagine out of thin air; it is established by God. We must, through spiritual cultivation, increase our virtue and wisdom to perceive it based on the similarity of things.

For this reason, the early Church Fathers often emphasized that all things ultimately point to some transcendent truth. One cannot read the Bible only literally but must combine it with spiritual interpretation. If you only care about natural things, you become a "slave of the sign".

In summary, Augustine advocated that "God enables us to know the world," while Aquinas leaned toward that "the world enables us to know God."

There are many reasons for this shift in perspective. One might be that the large influx of Romans into the faith diluted the original fundamentalist concentration; more ordinary people still had needs for secular pleasure and would place greater emphasis on matter and the body.

Another was the development of navigation. As human exploration of nature became more extensive, the original interpretations of the Bible began to show inconsistencies. Consequently, a group of scholars began to try to correct the errors in the commentaries of the ancient Church Fathers.

At the same time, Protestantism grew and said believers could read the Bible directly without only relying on Church interpreters, thus breaking the Catholic Church's monopoly on biblical interpretation.

Throughout this process, two concepts were in constant competition and opposition: one was Nominalism, and the other was Realism.

Let's return to the preface. What was mentioned at the start was an Aristotelian theological thought, which advocates that we come to know God by knowing the rules of the world. It focuses on the internal operating order of all natural things. In this way, we shift from "recognizing the similarity of things" (classification) to "recognizing the causality of things." Herein lies the problem: although this causality was created by God, God also does not violate it. This places a limit on God's omnipotence.

At this point, Ockham argued that God is not bound by anything, not even the rules He previously created, and said the very famous words: "Entities must not be multiplied beyond necessity." (Latin: Non sunt multiplicanda entia sine necessitate).

Here, "entia" refers to "universals" not "particulars". Instead of using old viewpoint, Ockham reckoned that "universals" are not real, eternal substances existing independently, but they are more like concepts or words, created by humans as tools for classification, and these tools are often language.

Ockham believed that God could not create universals because there was no need, and for humans, universals are merely fictional concepts. For example, "my right hand" as a concept is not "real"—it is not a thing. It is a position in a symbolic network used to refer to Thing C.

Humans cannot completely avoid relying on universals; even now, I am using these tools to communicate with you. But Ockham believed that every time we use such an established concept, we move further away from the truth, away from God. We should not add universals without necessity. This tendency is what we call Nominalism.

Opposing it is Realism. As we discussed in Part 2, Realism holds that the world has universal laws that can be known through reason and effort. In religious practice, it advocates that humans can attain salvation through good works and spiritual cultivation. This viewpoint is very easy to understand, so I won't explain it further here. The only thing to note is that while these two views are opposed, they also contain elements of each other. When one view pushes its position to the extreme, it inevitably finds that it has moved toward its opposite.

Yes, Nominalism is cool, but why do we mention it? Please recall Part 2: Augustine argued that "a thing itself, as a sign, points to other things". Words and things are mutual signs, and this forms a vast chain of reference among things: Thing X points to Thing Y, Thing Y points to Thing Z...

However, the Protestant revolution, guided by Nominalism, believed one should emphasize the direct, literal meaning of the Bible. The endless symbolic relationships of reference between thing and thing no longer exist. A thing can only point to itself. Reference became the exclusive feature of words. Only words can refer to other words. And most importantly, the latter referential relationship is a purely logical one; it is non-referential to objects(or things).

If we were to argue this difference in detail, it would make this already long guide even more verbose. I will only state the conclusion here. If you are interested, you can look up more materials yourself. According to Realism, the power of symbolism comes from the internal structure of the thing, it is something the thing possesses ontologically and is part of reality(Ockham, however, disagreed). In Nominalism, the power of symbolism comes from the conventions of language and rhetoric, it is something humans add onto the thing.

The emergence of the latter, in fact, separated word from thing, and transformed what was previously considered "eternal essence" into "flexible interpretation." Our understanding of the world shifted from seeking a single, fixed truth to making the most practical inferences based on empirical evidence. In this framework, we from belief in things to various extend based on what we already believed or assumed. This perspective is quite modern and remains influential even today.

As we separated word from thing, a new and serious problem appeared. If we accept that language confined to a purely inter-linguistic system, can only refer to another sign, our language risks becoming detached from the real world. How can a system built on human convention truly represent the non-conventional, external nature or essence of things?

About what we can know logically and what we can experientially capture is precisely what Wittgenstein attempts to address in Tractatus Logico-Philosophicus, which will not be covered in this guide of course.

To close, I’d like to leave you with a quote from Cortana in Halo 4, which, in its own way, touches on a rather similar issue:

I could give you over forty thousand reasons why I know that sun isn't real.
I know it because the emitter's Rayleigh Effect is disproportionate to its suggested size.
I know it because its stellar cycle is more symmetrical than that of an actual star.

But for all that, I'll never actually know if it looks real. If it feels real.