One of Sagan's last books, The Demon-Haunted World is a powerful call for reason in a world which is often dominated by irrationality. He takes up arms against a sea of fallacies, from witch trials to claims of alien abduction, and by opposing at least throws us a life preserver. The book is rather fragmentary, being a series of essays, but is consistently fascinating.

Sagan cites disturbing tendencies among most people to believe poorly supported ideas, and to fail to develop the faculty of critical thinking. He notes that polls indicate that large numbers of Americans believe that astrology is valid and that aliens in UFO's visit Earth regularly and abduct people. Students here, he tells us, are frighteningly ignorant of science. He discusses a psychic hoax set up by James Randi, which fooled large crowds and much of the news media in Australia before Randi revealed that he had set it up to test people's gullibility. He also gives accounts of horrible delusions of the past; his history of persecution of "witches" is brief but frightening.

The book addresses an issue which many critics of supernatural claims are reluctant to touch: claims made in the Bible. He points out that "[t]he Bible is full of so many stories of contradictory moral purpose that every generation can find scriptural justification for nearly any action it proposes -- from incest, slavery, and mass murder to the most refined love, courage, and self-sacrifice." (Whether self-sacrifice is in any sense "refined" is another question.) The Book of Deuteronomy is mentioned as a hoax which very conveniently served the purposes of its "discoverer," King Josiah. One quote is particularly amusing:

Surely we can understand why, in the anguish of an unwanted pregnancy, a teenager living in a society flooded with accounts of alien visitation might invent such a story. Here, too, there are possible religious antecedents.

Sagan holds a frustrating mix of political views. In many respects he is an ardent advocate of freedom, yet he seems to believe that government programs -- i.e., taxes and compulsion -- are the solution to nearly every problem. He eloquently defends freedom of speech, yet believes that government-subsidized science can somehow remain free and supports "experimentation" by governments. He suggests "a special education tax for those industries with special needs for technically trained workers" -- in effect, a tax penalty on advanced technology. On the positive side, I love his wish "that the Pledge of Allegiance were directed at the Constitution and the Bill of Rights ... rather than to the flag and the nation" (though requiring school children to take any kind of pledge of allegiance is contrary to the American spirit).

I do recommend the book; its qualities outweigh its flaws. But I would like to take issue in some detail with Sagan's approach to the philosophy of science. He presents a consistent view, one which is widely held among modern thinkers; but it is a view which has some serious flaws. Those of you who aren't interested in a major digression in the philosophy of science may want to stop reading here -- but please read the book anyway.

In Chapter 10, "The Dragon in My Garage," Sagan gives a hypothetical example of a bizarre claim: "A fire-breathing dragon lives in my garage." Every suggestion you offer for a means to verify the claim is countered by a still more arbitrary assertion. You ask to see the dragon; it's invisible. You suggest putting flour on the floor to get its footprints; it floats in mid-air. Likewise for every test proposed.

Sagan correctly asks, "what's the difference between an invisible, incorporeal, floating dragon who spits heatless fire and no dragon at all?" However, he suggests that if you are "scrupulously open-minded," then

you don't outright reject the notion that there's a fire-breathing dragon in my garage. You merely put it on hold. Present evidence is strongly against it, but if a new body of data emerge you're prepared to examine it and see if it convinces you.

To be rationally considered, an idea must have some kind of supporting evidence or reasoning. The idea might be consistent with just one observation, or might provide a very strained explanation for puzzling phenomena, but even that would be a starting point. If the argument behind it proves to be worthless, then it's back to being arbitrary and needs no further consideration until better evidence for it appears.

Sagan is, of course, trying to avoid dogmatic thinking. He notes that the claims made by relativity can seem just as arbitrary and fantastic, based on ordinary experience, as any dragon in the garage. There is evidence supporting relativity, but it is not the kind which most of us encounter or know how to analyze. Without willingness to consider the unlikely, we could never advance in science.

Still, the difference between an assertion for which support is claimed and one held in the absence of any support is crucial. The arguments for an idea may be difficult, flawed, dishonest, or merely inadequate; but some argument, bearing some slight degree of plausibility, is needed for the idea to qualify in the debate. If the advocates of a claim continue to hold it after all the evidence which they offer is refuted, they have no further claim on "a respectful hearing."

Sagan tells us that "absence of evidence is not evidence of absence." This dictum is valid and important insofar as it directs us not to reject ideas simply for being outside our normal experience. We often have to live with the absence of direct evidence; for instance, until recent years there was no strong direct evidence for the existence of planets outside the Solar System. But there has been indirect evidence for centuries, in our knowledge that there are countless stars similar to our own planet-bearing star.

This contrasts with the case of a proposition for which there is simply no reasonable support, such as the claim that stars outside the Solar System influence our lives by their position at the time we were born. In the last analysis, absence of evidence is the only evidence of absence; there is no way to demonstrate the effects or measure the qualities of a non-existent. When a claim is unsupported, we aren't epistemologically obliged to give refuting evidence before tossing it out.

The reason for Sagan's view evidently lies in a particular view of certainty and "absolutism." He states:

Except in pure mathematics, nothing is known for certain (although much is certainly false)...

Humans may crave absolute certainty; they may aspire to it, they may pretend, as partisans of certain religions do, to have attained it. But the history of science -- by far the most successful claim to knowledge accessible to humans -- teaches that the most we can hope for is successive improvement in our understanding, learning from our mistakes, an asymptotic approach to the Universe, but with the proviso that absolute certainty will always elude us.

If nothing is certain, then it's hard to see how anything can be "certainly false." Thus, we can't absolutely reject any empirical claim. But Sagan's view digs a trap for itself; he offers the impossibility of absolute certainty as an absolute certainty. The denial of all certainty cuts at its own roots, miring itself in inconsistency. Still, he is addressing a real problem: what we believe today may have to be corrected by tomorrow's evidence. We can't expect that everything which we believe today to be true will stand unchallenged by future knowledge.

The solution to this is to recognize that knowledge is relational and hierarchical -- that any claim of knowledge is made in a given context of prior knowledge. Leonard Peikoff writes in Objectivism:

Man is a being of limited knowledge -- and he must, therefore, identify the cognitive context of his conclusions. In any situation where there is reason to suspect that a variety of factors is relevant to the truth, only some of which are presently known, he is obliged to acknowledge this fact. The implicit or explicit preamble to his conclusion must be: "On the basis of the available evidence, i.e., within the context of the factors so far discovered, the following is the proper conclusion to draw." Thereafter, the individual must continue to observe and identify; should new information warrant it, he must qualify his conclusion accordingly.

If a man follows this policy, he will find that his knowledge at one stage is not contradicted by later discoveries.

But in the absence of any metaphysics, how do we recognize the validity of science? We can say that science works, that it produces predictable results, that we experience its successes; but these statements are predicated on the premise that our experience is valid, that our senses aren't being continuously deceived by some demon or mad scientist. In order to justify science, we must first justify a metaphysics of realism. (I raised this point in a letter to Skeptical Inquirer a few years ago, and some very annoyed responses appeared in a subsequent issue.)

If all hypotheses deserve some consideration, we're stuck; we can propose that the whole universe is a figment of your imagination, or that our minds are processes in a gigantic computer simulation, and who's to contradict the claim? "Absence of evidence is not evidence of absence." But if we take a contextual approach, we can recognize that there's something out there, and that it impinges on our awareness in certain ways. Broadening our understanding, we can recognize that reality is self-consistent -- that something can't be so and not be so at the same time and in the same respect.

This is a minimalist metaphysics, compared with the sweeping structures created by philosophers like Plato. It recognizes that the particulars of the universe around us can be identified only by specific observations and tests. But the difference between this metaphysics and no metaphysics is anything but minimal. If we have no assurance that science is anything more than a self-consistent body of faith (as some people of religious persuasions claim it is), then it's doubtful whether it has any real point at all. Sagan recognizes the difficulty at one point:

Attempts to reconcile religion and science have been on the religious agenda for centuries -- at least for those who did not insist on Biblical and Qu'ranic literalism with no room for allegory or metaphor... But how to do this where a clear dispute arises? It cannot be accomplished without some supervening organizing principle, some superior way to know the world.

The view that an understanding of the underlying reality is not necessary is expressed in a comment by Richard Feynman on Maxwell's equations, which Sagan cites:

Today, we understand better that what counts are the equations themselves and not the model used to get them. We may only question whether the equations are true or false.

At the same time, we have to be careful not to let philosophy intrude on the realm of science. From a realist standpoint, all that philosophy can say is that if "quantum fluctuations" led to the universe as it now is, then they were fluctuations in something. The only attribute which we're ascribing to this "something" is the ability to have such fluctuations, and thereby to give rise to the universe. But by recognizing that it's something which has this ability, some scientist might be led to the identification of further characteristics of this "something," and thereby to a better understanding of the origins of the universe as we know it.

Carl Sagan contributed a great deal to people's understanding of science. I've chosen to discuss his views of science in detail because they are among the best statements of today's dominant philosophy of science. But if science can be put on a more solid philosophical foundation, then it can accomplish even more, and perhaps provide a brighter "candle in the dark."

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Last updated: 12-Dec-2007