You can’t kill a virus, common wisdom contends, because viruses aren’t alive to begin with.
Yet some viruses sure act like they’re alive. And in fact, you can find biologists and philosophers who will insist that viruses do deserve a branch on the tree of life. Still, many other experts refuse to confer viruses with life status.
Debates about viruses as life-forms (or not) have raged for decades. But as more and more data on viral vitality accumulate, the disagreements do not diminish. Perhaps that’s because the argument is not really about the nature of viruses. Rather it’s about the definition of life. Scientists can’t agree on that, either.
Science’s inability to define life reveals not merely a lack of lexicographic dexterity, but also signifies a broader issue — the peculiar way that science’s relationship with reality is connected to science’s relationship with words.
Words are obviously indispensable for scientists, both to communicate among themselves and to report their findings to the rest of civilization. Even in the most mathematical of sciences, words must be attached to symbols in order to relate mathematical relationships to real-world phenomena. Words like energy or force or stress tensor describe a physical entity corresponding to a symbol in an equation.
But many scientific ideas do not reduce to a neat mathematical expression, so the words are on their own. And sometimes the ideas originate with the words. Throughout history, scientists have often coined a word before fully formulating the underlying idea. As Johann Wolfgang von Goethe wrote in his poetic play Faust, in the absence of ideas, words can come to the rescue. “With words, the mind does its conceiving,” reads one translation. (Or, in another version, “If your meaning’s threatened with stagnation, then words come in, to save the situation.”)
So sometimes scientists adopt a term, and use it widely, even though no precise definition of that term is universally accepted. Life is an obvious example. It’s a word that most people instinctively understand yet nobody can define to everybody else’s satisfaction.
“We all think we can recognize a living organism when we see one,” biochemists Athel Cornish-Bowden and María Luz Cárdenas wrote in the February issue of the journal BioSystems, “but it is not so easy to give a definition of ‘living’ that includes all the entities we consider to be alive, and excludes the ones we do not.”
Some proposed definitions of life, for instance, include the capacity to reproduce, note Cornish-Bowden and Cárdenas, of Aix-Marseille University in France. Sounds good, but what about mules? They can’t reproduce, but most people would agree that mules are alive, the biochemists point out. “Taking the minority view that mules cannot be regarded as alive does not solve the problem, because many people, including many distinguished biologists, have passed the age when they can reproduce, but would dispute any claim that they are not alive.”
Life is one of many common scientific words that elude precise definition. And scientists have often used much vaguer terms, typically as stand-ins for primitive, imprecise ideas — some that turned out to be in essence correct, others totally wrong.
Ancient Greeks, for instance, invented the word atom to describe the tiniest, “uncuttable” pieces of matter. But no Greek had any real knowledge of what an atom actually was like (and of course, they had no proof that atoms even existed, as atom denier Aristotle vigorously argued). But the concept turned out to be roughly right. Chemists in the 18th century, on the other hand, insisted that fire depended on a substance called phlogiston. But phlogiston was just a word, linked to an idea that turned out to be completely erroneous. Similarly impetus, a term popular in medieval times for discussing Aristotle’s views on how objects in motion kept moving, lost its momentum once Galileo and Newton debunked Aristotle.
In more modern times, the word gene, like atom, initially described a primitive idea, not yet fully formed. (Gene, referring to an element of heredity, was coined by the Danish botanist Wilhelm Johannsen in 1909, decades before anybody knew how DNA worked.) Over the last century the definition of gene has evolved, though it’s still not as rigorously defined as all scientists would like.
Part of science’s problem in linking words to meanings is (as experts in language repeatedly remind us) that there’s always a gap between a word and the reality it represents. “The word is not the thing,” the semanticist S.I. Hayakawa emphasized in his famous book Language in Thought and Action, just as a map is not identical to the territory it depicts. Some scientific terms serve as pretty reliable maps of reality, while others turn out to be decoys leading to dead ends. A major part of scientific progress is narrowing the gap between word and thing — transforming vague labels into more specific symbols.
It’s easy to find many current examples of scientific terms that mimic knowledge while actually disguising a lack of understanding. “Dark matter” and “dark energy” must exist, physicists insist, while admitting nobody yet can say what they actually are. Other deep mysteries baffling today’s best scientific detectives also reflect an inability to bring words closer to things. Consciousness is a prime example, referring to mental processes that have eluded anything approaching a coherent physical description. Intelligence comes a little closer to intelligible meaning, but not sufficiently to avoid all sorts of arguments about reproducing it artificially.
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Another favorite problem word for physicists, time, poses a plethora of puzzles. For one thing, it has multiple meanings — time of day is not the same thing as period of time is not the same thing as time travel. Physicists still squabble over why time’s arrow points only to the future and whether the flow of time is an objective physical fact or an illusion in a “block universe” where all events are already sitting there, just waiting for a conscious observer to witness them. Of course, it may turn out that time’s mysteries are problems more of language than of physics. “We run into puzzles about the concept of time and then we say, oh, what a terrible thing,” the physicist John Archibald Wheeler once said. “We don’t realize we’re the source of the puzzle because we invented the word.”
Only time (another meaning) will tell whether words like time and consciousness express ideas of greater depth than scientific understanding has yet reached. Maybe consciousness and time will turn out to be prophetic terms, like atom, that foreshadow the emergence of reliable scientific concepts. Or maybe time and consciousness (and who know what other words) will go poof! like phlogiston.
In any case, it’s remarkable how often words masquerading as ideas can eventually lead to successful scientific endeavors. Entire fields of scientific research have grown from word-seeds invented in the absence of substantiated ideas — atom and gene being the best examples. As Goethe went on to note in Faust:
“With words fine arguments can be weighted, with words whole systems can be created.”
But it might be a good idea to remember that the character speaking those lines was Mephistopheles, Goethe’s representative of the devil himself.