Science only acknowledges senses for the material world: you see, you hear, you feel, you smell, you taste. But how is it that we can also sense how we feel inside? We are able to quiet the mind we can perceive sensations which have nothing to do with the material world: the tingling of aliveness, a lightness or heaviness in the heart, our biological urges. When the outer landscape recedes, the inner landscape emerges naturally.
This way of sensing inwardly is an introversion, which, through considerable effort, allows us to observe what is going inside our mind. We might be initially afraid to even peek inwardly, and with good reason: exploring the inner maze is not for those faint of heart.
When we first encounter these lands, we ignorantly believe they are our own property. We might feel we are sad, which inwardly feels like a cold drizzling overcast day, and believe that by our own will we can make the clouds part and have the sun shine on us. We say: "put on a smile and think positively!" but when the sky fails to clear we think it is because of our own incompetence in controlling our emotions.
The part of our inner world that is under our control is paralleled by the material world. We are not able to control the weather, but we are able to provide shelter for ourselves. We can't make the clouds part and the sun shine over us, but we can sit comfortably inside our homes sipping tea while we watch the rain.
Yet, because we are ignorant about inner matters, instead of putting effort into our homes, we raise up our fists and scream to the sky "stop raining, I want it to be sunny!".
In the 16th century, at the age of 38, Michel de Montaigne retired from public life and isolated himself completely from the outer world into a tower filled with books. He wrote the Essais, an intense and honest introspection into his soul. In seclusion he expected to put his mind in order, instead he finds this:
[My mind] is like a horse that has broke from his rider, who voluntarily runs into a much more violent career than any horseman would put him to, and creates me so many chimaeras and fantastic monsters, one upon another, without order or design, that, the better at leisure to contemplate their strangeness and absurdity, I have begun to commit them to writing, hoping in time to make it ashamed of itself.
Here is the crux of inner exploration: a non-judgemental curiosity about what happens inside of us, not desiring to control but to understand. In this way of perceiving the world, you are more intrigued about your reaction to an event rather than the event itself. If someone annoys you, you don't think I wish this person would leave so that I can regain my serenity nor I shouldn't be annoyed at this person but ah, that's interesting, what is it about this person that makes annoyance arise in me?, observing emotion from a place of non-identification.
When you read philosophy classics of antiquity it is evident that this way of knowing has been largely lost in modern times. In a world that had little recorded knowledge, no mass media, and a generalized lack of information, it is amazing that the thinker of antiquity was able to deduce a large amount of knowledge through inner exploration, simply by following the advice inscribed at the temple of Delphi: ΓΝΩΘΙ ΣΑΥΤΟΝ, Know thyself.
Where the philosopher of antiquity lacked in information about the outer world, he made up in tools he had to access inner knowledge. With a rich model for the composition of the metaphysical parts of the psyche: logos, spirit and soul, the philosopher had the necessary tools extract knowledge from himself. He would not use this precious information to gain power, riches or any other selfish motive (those were sophists), but instead would explore within "on the behalf of the many", in words of Buckminster Fuller (edited for clarity).
In 1927 when I started to explore for the faculties with which we are all endowed, I was doing so only for one fundamental drive: because I had considered suicide, I decided that my warrant for not committing suicide was that I would turn my experiences to the advantage of others. Whatever I have been able to uncover of these faculties comes from wishing to employ them to the advantage of the many.
The self-centeredness of the spiritual quest ultimately turns inside out. As Ramana Maharshi famously states: "By the inquiry 'Who am I?', the thought 'who am I?' will destroy all other thoughts, and like the stick used for stirring the burning pyre, it will itself in the end get destroyed. Then, there will arise Self-realization".
This the most paradoxical aspect of the spiritual quest: the work you perform on yourself is ultimately for others. Though the act of inner exploration is deeply intimate, it ends up connecting us to all of humanity, because the things you feel and sense inside are the same things everyone experiences, and thus by understanding yourself you end up understanding others.