My everyday language would suggest that I have many beliefs which I do not. I don't believe in free will, yet I speak as if I do. I can doubt the validity of just about everything, yet my sentences are written as if I am certain about the statements I am making. I live with the ambiguity. I speak the way I do partly because that is the way English is structured, but also because our minds are trained to think as if we have free will and as if we are more certain about things than we can be.
Believe me, the irony is not lost on me.
I first read Rene Descarte when I was in Middle School. I think he is right in that nearly everything can be doubted. We very well could be in the Matrix in which everything we think is real is actually just computer software, or something else. If we see a table, feel a table, taste a table, hear a table, etc, all we have shown is consistency, not that it exists in reality. Descarte said that the only thing that he could not doubt is that he is doubting. He then coined the phrase, "I think, therefore I am". I believe that he did not go far enough. I think that I can doubt that I am doubting. I suggest that all we can know is that something is happening. So, there you have my core belief about certainty.
Now, in everyday life, acknowledging that there is little we can know for certain, I take an interest in this "something" that I perceive. I assume, fully recognizing that this is an assumption, that this world is real. Now, if it is real, I ask myself what can I learn about it. Through systematic observation, will we be able to detect some consistencies or patterns? Might we be able to organize our data and through inductive reasoning describe natural laws? Might we test our reasoning by making predictions about future observations? We refer to this process as science. I feel that science is the best tool we have to learn about this world we live in. It is not perfect, but I believe it is the best tool we have.
So, is truth about reality knowable? I do believe that an objective reality exists. I believe that we might come close to discovering the truth about parts of that reality. But, because we can always doubt that are findings and thinking on a particular subject reflect reality, I would suggest that we will not be able to "know for certain" that we are right. Therefore, I would say that the truth about reality is not likely to be knowable, although we may discover the truth without ever being able to be certain that we are right.
(Note: Did you catch those certain statements I made? I caught them, too. If I reword all of my sentences to reflect the uncertainty that I believe in, the sentences would become very difficult to read. So, now that you know where I am coming from, paint this whole post with uncertainty.)