I was not a science major but I have read a lot on my own, and one of my heroes of rationalism is Carl Sagan. He wrote a book called Demon-haunted World: Science as a Candle in the Dark.

I love the book but I wonder why Sagan did not use a more powerful metaphor. A candle is so small. Why not a sun? Or at least a flashlight? Or a lantern? I suppose neither of the last two sound as poetic as a candle.

Nor as humble. A candle flame seems like a metaphorical nod to vast areas of dark uncertainty that the light of reason and observation may never be able to reach. Still a candle is powerful. If you touch it, it will burn you. With enough fuel, it can become a conflagration.

The humble candle metaphor seems fitting for the kind of thinking Sagan promotes: allowing the universe to tell you what it is like rather than forcing wishful thinking or irrational preconceptions onto it. Science is gentler than a blowtorch; more questing, like a candle, yet still powerfully illuminating.

Having bipolar disorder, I am always looking for ways to apply that kind of thinking to my personal life. My moods affect how I see the world. Medication makes mood swings more manageable and less intense, but at times they still occur and affect my perspective.

When I am in a bad mood, I filter out all the good and have trouble seeing beyond the moment to a time when I will feel better. When my mood is soaring, I filter out the bad. I feel enlightened, confident, and creative; it seems that nothing can go wrong. When my mood soars I tend to assume that people like me. When it falls, I more easily imagine criticism.

Having a mood disorder is like viewing the world through a window of distorting glass, and one that is always changing. Even when you know that the glass may be distorting things, the illusion remains powerfully intact.

Reality seems slippery, partly because I am unable to experience the world directly. Everything I know is filtered through mental processes that include preconceptions, memories of past events, wishful thinking, and emotion.

Because I know these distortions exist, I am constantly trying to correct them when they occur. Maybe if I use enough logic, enough objectivity, I can straighten out the uneven glass of my emotional windows. Of course, it is not that simple. Bipolar disorder has a large biochemical component, which is why medication helps.

But it is not just those with mental disorders whose perceptions are distorted through filters. To varying degrees, everyone lives behind a distorting glass.

I recently watched a show about optical illusions. Our brains are constantly tricking us into seeing things not really there, making us think one color is another, for example. Color itself is an illusion. It has no existence outside of human perception. Color is something the brain creates to enable people to get around in the physical world.

There are many other things that keep perfectly sane people from seeing reality as it is: uncritically accepting false information; unreliable memories; monstrous egos; wishful thinking; or blind faith.

When I had my severe manic episodes, I had no choice but to believe things that were untrue. I was essentially dreaming while awake. When I got over my episodes I was horrified by some of the outrageous things I had believed when I was at my worst.

But many mentally healthy people I see are willing to surrender their critical power to cross reference their illusions with their observations. Bigots are too often reluctant to let go of their prejudices, even when their observations contradict them. Others embrace pseudosciences such as astrology, the magical power of crystals, faith healing, or channeling the dead, even though there is inadequate empirical data to support them and they do a bad job of predicting outcomes.

Although the scientific method has an excellent track record for making predictions about the natural world that are made practical in the form of technology, many people are wary of it.

But how much does it matter? What difference does it make what people believe is true, as long as they can go about their lives and work and raise kids and buy groceries and eat? What practical difference does it make if people believe the world is 6000 years old instead of 4.5 billion? Or even if they believe the earth is the center of the universe? Does seeing reality as it truly is matter?

It matters to me. It matters to me in part because I have experienced the extremes of being out of touch with reality, and not by choice. To me, being irrational means a willing move toward mental illness, while reason anchors me to reality. But reason means accepting some uncertainty. Sometimes uncertainty is uncomfortable, so I try to guess what people are thinking. It never works and only causes stress.

Controlled studies are not practical in the realm of reading minds, but there is an aspect of science I can apply to my personal life: objectivity. Objectivity means acknowledging uncertainty where it exists and resisting the temptation to project fantasies onto it.

In both science and my life, I want to know the world for what it is. Reason may not be enough to lift the veil from every mystery or turn every unknown into a known. But it is something. It is a gateway into reality. It is a humble, questing flicker in the void. It is a real but subtle power.

It is a candle in the dark.