Theine IS caffeine, 1,3,7-trimethyl xanthine. When tea came to Britain, coffee houses had an unsavory reputation. It was known that both coffee and tea contained a stimulant of some form, but modern chemical methods would not be discovered for hundreds of years. Since tea was considered suitable for consumption by women and decent people (and women were not yet people), the stimulatory substance in tea was widely accepted culturally as different than that of coffee.
Fast forward a couple hundred years, and the means to determine chemical structure get their infancy in the latter half of the nineteenth century. Still not as capable as modern methods, the chemical identity seems similar, but because the expectation was that there must be some difference, it is given its own name on the assumption that once discovered, it will make the difference “make sense”
We have had the advantage of modern methods, but there is still this large body of copyright-free, older primary and secondary sources asserting and “proving” they are different. From a Wikipedia editor type point of view, there's enough secondary material easily sourced from seemingly reputable sources stating that there is a difference. I've seen researchers publish that the difference isn't chemical, per se, but due to theanine or tea catechins or some other factor that is different in tea a priori, but coincidence is not proof. So the theine shibboleth continues to propagate in primary and secondary literature, and is unextinguishable in Wikipedia like governance.
So again and again, these kinds of questions get asked. But don’t just take my word for it, because that too is a fallacious argument, argument by authority. This kind of problem is almost inevitable in modernity, where nothing is ever forgotten and long chains of evidence are costly to replicate. This sort of problem needs a different critical mode, in which we consider the historical chain of evidence as antithetical to gathering truth, even while closely examining it.
And, there's a limit on science, often referred to as scientism, where evidence presented in the form of scientific research (notably, when it is a ruse, like Nazi science, or less clearly a ruse, as the difference between theine and caffeine, and dozens of other examples I can name off the top of my head) is given higher standing and respect than other modes of thought. That is not to say there is a better way to do what science attempts to do (determine cause), but that in doing so we run the risk of creating or propagating error indefinitely due to false certainty. Because as we commit opinions to paper, it makes them indelible upon society.
Computerization and the redundancies of the Internet are making this worse. Detecting plagiarism, for example, is less a problem of comparison as it is a “p not np” type problem where comparison grows combinatorially, n!, even as infotech grows exponentially. Translation makes this worse: if a cultural word like theine or caffeine were explained to a space alien, the translator has an opportunity to side in that debate.
The difference between theine and caffeine, to the casual reader, seems petty and insignificant. But, it is a simple introduction to the problematic legacy of the twentieth century, and pervasive within that legacy, and potentially suicidal for “immortal” technology. Like racial epithets, we don't need them to communicate effectively, and what we need is a sort of memento mori, so that when future generations ask, we can cite these dead terms on proper grounds for dismissal.
Like this: the-ine: archaic, see caffeine.