Thus we cannot point to any one thing as the root cause of my idea of greenness. The fact that the frog continues to appear green every time I look at it and has done so consistently for the past 20 years seems to indicate that the frog possesses some attribute that consistently contributes to its appearing green. It also demonstrates that the photons of light continue to react to that attribute such that the light continues to reflect with the same wavelength. Thus the properties of light remain consistent. In addition, the rods and cones in my retina consistently react with the light. So we have all these reactions that occur consistently over what seems to be long periods of time.
This consistency has enormous significance that I'll examine more later. But as for the knowledge imbued from sense experience, the frog's green appearance does not tell us much about the frog itself except that it has some attribute that reacts in a consistent way with light. Also, that light has attributes that react in a consistent way with our retinas, and so on. We do not know what it is inherently about the frog that causes it to appear green. It has as much to do with the properties of light and our eyeballs as with the frog.
This same point applies to all five external senses. They can all be reduced to interactions that begin with the features of the object, which are then affected by the features of some conveyance to the subject, and then are further affected by the features of the subject itself. The net result tells us little about the object itself other than its composition is consistent. We cannot know even this conclusively however, since it is still possible to imagine that the properties of the object, conveyance, and subject are simultaneously and continuously changing in such a way that the net result is always the same. But this seems so unlikely that we do not seriously entertain it. Nonetheless, we cannot disprove it.
Thus sense experience is useless for understanding objects as they are in themselves. Some have gone so far to suppose that we have no business even asserting the existence of objects (as with Berkeley). All we know is the net result of these interactions. All I know is that there appears to be a green object on my desk, but this appearance is merely a reaction within me. Thus we cannot say that the object necessarily exists on its own apart from me, but simply that my environment is such that it interacts with my brain to produce these ideas. We end up with a distinction between ideas in our consciousnesses and what we suppose on faith to be an extra-mentally existent world.
We are then faced with a choice:
1 - We assert that objects do indeed exist apart from our ideas of them, but that we cannot know the essence of those objects. All we can know is our sense experience, which provides data that is an aggregation of the features of the object, the conveyance, and the subject combined.
2 - We assert that objects do not exist apart from our ideas of them; that all we have are our ideas, and nothing more. This has led to idealism [the philosophical theory which maintains that experience is ultimately based on mental activity], which attempts to make this assertion while avoiding solipsism [the philosophical idea that only one's own mind is sure to exist.], which they achieve by asserting a pantheistic force or God figure that essentially controls all of our ideas. Without the God figure or force, we slip into solipsism and nihilism [the philosophical doctrine suggesting the negation of one or more meaningful aspects of life.].
It seems to me that #2 does not allow for free will; we are just playing out a drama controlled entirely (and I mean entirely) by a pantheistic force of some kind. To me, this still leads to nihilism because my thoughts, beliefs, and actions are not my own. They are God's. And there is no sense in speaking of morality since my choices and actions are predetermined. I have no control over my relative happiness and well-being; we are all entirely at the mercy of whatever "the force" decides for us. (This may be where my predispositions come into play, but I just don't believe this.)
So I choose #1. And this "choice" (inasmuch as I can call it that) is not based solely on avoiding nihilism. There is more to say to help justify it, and this will come out in future essays. Although I admit in advance that my arguments do not "prove" it in any strict sense, but simply reinforce it. The rational exigency returns to avoiding nihilism in the end. And not to belabor the point, but I see this as necessary and reasonable. Nihilism makes for a fine academic discussion, but we should not discount or underestimate the very real and very harsh consequences of nihilism in practice. I genuinely believe that "nihilism is death." And I will stand behind a line of reason that regards avoiding nihilism as foundational.