One way to dismiss an idea is to insist that it “is just a theory.” However, the point of calling something a theory is that it is a proven explanation. This doesn’t mean it cannot be changed, improved upon, surpassed by another theory that explains more and in better ways. When a concept is a theory, however, it sets the terms and relations necessary to improve or even overturn it.
Three examples of theories changing
The first is phlogiston. First introduced in the 17th century, this theory attempted to explain how things burn, and why they stop burning as well. Things which are liable to burn have a substance, the theory went, that escapes during the burning that it causes, until the air around it becomes full of this “phlogiston” (meaning “burning up”), thus stopping the fire. When this process happened slowly, it explained how rust formed. As a theoretical explanation, however, it got people thinking about how to prove it, or improve it. One fact that it could not explain was that, for instance, magnesium when burned weighs more than it did before being burned. Eventually Antoine Lavoisier proved that fire (and rust) are actually caused by oxygen, a substance not in the object being burned or rusting, but in the air. Rust is “oxygenation”, and fire is very rapid oxygenation.
Without the theoretical explanation, though it was wrong, chemistry as a whole would be significantly less advanced than it is today. The phlogiston theory did explain some things, for instance, the connection between rust and fire. In this way, it set up the terms of its own overturn.
A second example is the theory of relativity, first proposed by Albert Einstein in 1905 (“special relativity”) and completed in 1916 (“general relativity”). In fact, general relativity is a model worked out mathematically from the premises of special relativity. Those premises in turn were a magisterial summary of previous work by a number of scientists and mathematicians throughout the nineteenth century. “Relativity” refers to the fact that we cannot locate ourselves in space other than in relation to other bodies: there is no fixed center. The theory supplanted Isaac Newton’s theory of mechanics by introducing a corrective: for very large objects, their gravitational pull deforms space and time, a little like a cannonball placed on a trampoline.
In order to prove the theory, which as a model had made a set of predictions, experiments and observations had to be devised. Einstein’s theory predicted that light from distant stars would be distorted by nearer stars’ gravitational pull on space. This so-called “gravitational lensing” is now a constant of astronomy. Relativity equations predicted perfectly how to compensate for measurements that hitherto had been imprecise: the exact orbit of Mercury, the exact diameter of the Moon’s shadow on the Earth during an eclipse, and others. One aspect of this “backing into” reality through modeling is that, should any single prediction of the theory be proven false, the whole theory is false. So far, it has held up, although it does not explain quantum physics.
Darwin vs. Wallace
The third example of theory is, as you might have guessed, the theory of evolution.
Evolution is the brainchild of more than one person. Although Charles Darwin’s book The Origin of the Species is the classic text, Alfred Wallace had proposed it before he did. Based on zoological observations, both men concluded that the vast variety of life-forms on Earth is the result of changes or mutations of species as time progresses. From the simplest one-celled animals 3 billion years ago to a blue whale today is a jagged line of progression, in which species come in and out of existence as they adapt or fail to adapt to changing environmental conditions — by “natural selection”. This progression explains how, among other animals, human beings came to be.
The fossil record insofar as it goes backs the theory. One can trace the differentiation of animals and plants as time goes on and conditions change. The dinosaurs evolved into a huge diversity of reptiles, from as small as a rat to the largest creatures ever, the titanosaurs. The small mammals that managed to survive a hypothetical extinct event some 65 million years ago became dominant through evolution, finally producing the most dangerous and adaptable predator ever, namely, Me and You.
None of these is “just a theory.” The point of calling something a theory is that it is an explanation whose proof you can point to. This doesn’t mean it cannot be changed, improved upon, surpassed by another theory that explains more and in better ways. When a concept is a theory, however, it sets the terms and relations necessary to improve or even overturn it.
Wallace, toward the end of his life, began to have doubts that evolution was as explanatory as then believed. While the theory does seem to explain the variations of the fossil record, and varieties of species and how that variety comes about, Wallace claimed it does not explain human consciousness, in particular the linguistic and cultural fruits of humanity’s self-awareness. This has been increasingly criticized even by Wallace’s admirers, as he seemed to add a spiritual dimension to otherwise fine scientific work.
However, Wallace did not conclude that human intelligence, moral and ethical considerations, artistic creation, or the symbolic communication common only to human beings, and so forth, come from a divine intervention. He thought these were manifestations — facts — that natural selection did not cause but that other unknown factors were responsible for.
For example, I argued elsewhere that language did not evolve physically, but is rather a development of human culture over time. Wallace’s other considerations may or may not fit that explanation. One aspect that is overlooked far too often is the overall direction or arrow of evolution, which produces brains that project minds that theorize:
So far from consciousness or human intelligence being a somewhat embarrassing excrescence on the surface of rational material processes, it would appear to say that intelligence is literally the only phenomenon in the universe that makes sense of the overall direction of material existence towards coherent, sustainable, innovative adaptable forms.
And there is still a great deal to be learned, not only about that “direction” but also about the intellect we each possess, and the consciousness that allows us, for time to time, to be able to “catch the mind in the act” of thinking.
For from that work to develop and prove theories that are not “just” theories, but pointers to what is, in fact, Real.
[This story, along with “Just what is common sense?”, “Just what is meaning?”, “Just what is truth?”, “Just what is language?”, and “Just the facts, Ms. AI”, are excerpts from my unpublished book, Set You Free: Know Your Own Mind. Write me for more information…]
 In fact, Wallace had sent Darwin a manuscript asking him to send it on to experts. Instead, Darwin plagiarized it.
 Rowan Williams, The Edge of Words: God and the Habits of Language (London: Bloomsbury, 2014), page 102.