Skoyles's second argument is hard to grasp. He says, simply, that ideas people have in 1987 differ from those people had in 1933 and 402 BC. Ideas get replaced, it seems. And the replacement is not arbitrary: 'successful ideas gain their success because they possess characteristics not possessed by those ideas they replace. It might not seem like competition' but it is, Skoyles wants us to believe. I am mystified as to why a person would want to insist that ideas do compete, even that it is a fact that they do, at the same as admitting that it does not seem that they do. Certainly, it cannot be an argument in favour of the idea that ideas compete, that, while not seeming to compete, some ideas get replaced by others, unless Skoyles thinks that the only possible explanation of the replacement is that the ideas have competed, contrary to appearances, with some losing while others won. (Of course, he would also have to say where any new ideas came from, and that might drive him towards my theory.) But there is another explanation. There are probably several, but here is mine.
On my explanation, there is also a competition, but it is between people. People with certain ideas compete with people with different (perhaps, also, incompatible) ideas in an effort to gain followers or adherents or co-conspirators or just friends or power and prestige or the Nobel Prize. Let me explain why this is possible. Some ideas that people have are very difficult to test against the facts. The idea that ideas compete is one such, but any of the ideas that science has left for philosophers to argue about will do. Others are much easier to test, such as that water boils when heated and freezes when cooled or that bread nourishes. Or any of a thousand ideas that early scientists made it their business to investigate. It is an uphill battle getting much popularity for ideas that are easily shown to be wrong, once someone has found out how to show them wrong. It is much easier to gain adherents for ideas which cannot be shown up easily and which at the same time have a certain logical power. Ideas that solve painful puzzles or that bring coherence to one's personal pool of ideas are particularly welcome. So that if someone does or says something that suggests such an idea to me, I shall be inclined to believe him or her. Ricoeur remarked a while ago that if ideologies were to take popular hold they had to oversimplify things. Of course. The ordinary person can hardly be expected to come up with very complex and many-layered ideas in an effort to match a passing preacher's wayside or workplace utterances.
But we have to be careful, here, about when one idea is the same as another or when two people can both have the same idea. For my money, this last expression is loose talk. Two people can no more have the same idea than two people can have the same genes. Identical twins or clones can have genes that embody the same patterns,though their actual material genes are numerically distinct. Similarly, two people may have occurrent ideas that are numerically distinct (one being entertained in one mind and the other in the other) but share logical content. The logical content of an idea lies in the realm of possibility and is eternal. Actual ideas that you and I entertain are fleeting. Sometimes we remember, sometimes we forget. It is perfectly possible in a society for no-one at all to have any idea with a logical content that was once upon a time more or less exactly shared by ideas everybody had. It would be a manner of speaking to say that such an idea died. It is more exact to say that everybody who entertained ideas with that logical content died. We also talk about ideas reviving or being revived. I do not have any trouble with this metaphorically. On the account I am giving, talk about ideas being alive and competing and so on resembles talk about computers thinking or playing chess. A pretty shorthand for ideas whose more exact expression would be cumbersome.