A long time ago, there was a philosopher names Renee Descartes. He wrote a work called The Meditations. In it, he proposed to start from scratch to figure out what was really true. Now in philosophy there are two kinds of truth. A posteriori is what we think about as truth in modern terms. Scientific, or empirical, truth is known from experience; which is why science does experiments. If we see something happen a bunch of times the same way, we call it a fact. The problem with this kind of truth is that it is truth with a small "t". There's always a chance it can be disproved if we have an experience that contradicts it. For example, we can say that "fire is always hot", but if we ever felt a cold fire that statement would be proven untrue. There is nothing inherent in fore that says it has to be hot, we've just always experienced it that way. Descartes was looking for what philosophers call A priori truth (with a capital "T", conversely), that is, something that cannot be unproven because the fact is inherent of our understanding of the subject. A statement like "a triangle has three sides" will always be true because we could never hope to find a four sided triangle. It would obviously be a square or a rhombus, or some type of parallelogram. Anyway, that little foray into Philosophy 101 is to set the stage for Descartes.
He wanted to find something that was undeniably true aside from our senses and experience. He would eventually become the father of a whole line of thought called Rationalism. Western Philosophy really then breaks down into two camps at that point. Rationalism (which was more popular in continental Europe), and Empiricism (more popular in the British Isles). But back to The Meditations. Descartes eventually arrives at the point that he cannot doubt his own existence. This becomes the basis of all the other truths he claims to uncover afterwards. This is the one True fact that he cannot deny. He famously wrote it in Latin, "Cogito ergo sum." Which roughly translates into I think therefore I am. As he works through his meditations, he finds that he while he can trust in his own existence, he can still doubt everything around him. Anything he knows through his senses, his body, other people, the entire outside world, are things that he can only know conditionally. He can therefore find reason to doubt their existence. This sets up what is later referred to as Cartesian Dualism. Essentially, there is a fundamental difference between the self and everything else: the True and the doubtful. He eventually uses God as his go between. He cannot bring himself to believe that an omnibenevolent or "all good" God would choose to deceive him. He also says he cannot doubt God since the idea of an infinite being has to originate from an actual infinite being, since a finite, or limited mind, his self, could not conceive of an infinite or limitless being on his own.
I think this dualism has set us up for what we call the postmodern condition. We believe ourselves to be something different than the rest of the world. This has the potential of leading the human self to be separate from everything around it. It can lead to a real sense of loneliness. I think this is the reason so many of us, while so connected through technology and our daily interaction with others can feel so isolated, so alone. We don't see ourselves as a part of creation, but as a single entity, that has some privileged view of the world that no one else can experience.
True knowledge then comes from the realization that we are not alone. Our world is shaped through experience and interaction. Our self, or soul, is affected by the things that happen to us and around us. And thanks to the Christian viewpoint, we are most definitely not alone. Christ plays an intimate role in who we are, and has an infinite desire to shape us into the best version of ourselves. We have all been invited to play a special role in the salvation story. We are not merely individual selfs on a journey through an isolated life. We are called to be Christs for each other. We need the other in order to realize the true potential of who we are. This, in a roundabout way, leads us back to Descartes juncture in his reasoning. It is through God that we can begin to see the connection from our undeniable self to the rest of the speculative world. We realize that we are not special because we are a singularity in the universe, but that we are deeply connected to the universe through our connection to God and the Sacred Heart.