Not an optimist. Not a pessimist. A hopeful scientist.

In a world that's filled with bad news, a constant barrage of current outrages, and coming disasters, I am generally unworried.People who listen to these reports and believe them are pessimistic, and it's easy to see why. When I tell them that I am not pessimistic also, they accuse me of optimism, as though this was some sort of character defect. But, I explain, the fact that I'm not pessimistic does not mean I'm optimistic.

Is the glass half empty or half full? A pessimist would pick half empty, while an optimist would choose half full. An engineer, the story goes, would say that the glass was twice as large as it needed to be. A scientist would report only what was testable: that the 300 ml glass contained 150+/-3 ml of water with 99% confidence.

Unless I see the predicted doom as inevitable--and there is nothing that is truly inevitable--then I am hopeful, which is often taken for optimism. But it's not. I can be pessimistic and hopeful or optimistic and hopeful.My degree of optimism or pessimism is based on my assessment of the probability of either outcome, my degree of certainty about the probability statement, and whether I believe the likely outcome will ultimately be bad or good. In most cases the probabilities are uncertain. In the minority of cases where the probabilities run strongly for a bad outcome, then I will be pessimistic (though hopeful). If they run strongly for a good one, then I will be optimistic (though guardedly so; things can always go wrong.)But in most cases, I can't make a high-confidence prediction. That’s first because there's no good basis for making a prediction, and secondarily because while first-order effects can sometimes be predicted, there are often second-order an feedback effects that may offset them. For example, one might consider a reliable prediction in the price of oil prices to be a bad thing, but one consequence of such an increase might be more investment in sustainable energy, a good thing.For me to take any prediction seriously, it has to be scientifically credible. That means there must be a well-defined method for making such a prediction, and the method must have been tested many times, very thoroughly, and have been found accurate.

There is a vast difference between successfully predicting a future outcome, and successfully demonstrating that had the method in question could have successfully predicted the past, from a still earlier past time that viewed that past as its future.The "ask the expert" prediction technique is testable: see what that has expert predicted in the past, and measure how accurate have those predictions have been. Sadly, the answer, found by Philip Tetlock, is that most experts are not very good.

The world is uncertain.

But as long as it's possible, even if improbable, that things will work out I will remain hopeful.