How “HIV is the cause of AIDS” is true
A case study in meta-rational epistemology.
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“HIV is the cause of AIDS” is true, with nearly perfect certainty. This knowledge has great practical importance.
“What does ‘true’ mean in this case?” sounds like a dumb question:
“HIV is the cause of AIDS” is true because HIV is the cause of AIDS.
Here’s the thing, though. You may not know this…
HIV is defined as “various unrelated viruses that cause AIDS.” And AIDS is defined as “various unrelated diseases that are caused by HIV.”1 Substituting equals for equals, “HIV is the cause of AIDS” means:
Various unrelated viruses are the causes of various unrelated diseases.
Undoubtedly true. But nearly meaningless! And it says nothing about either HIV or AIDS.
There would seem to be some sort of a problem here.
Suddenly, the question “so, then, what does it mean that HIV is the cause of AIDS?” seems pressing. And, if even its meaningfulness is called into question, asking in what sense it could be true also doesn’t sound so stupid anymore.
The situation is highly unsatisfactory logically, but it works perfectly in practice—for specific reasons I’ll explain in this post.
I began In the Cells of the Eggplant with this very problem, in its first chapter:
What do “truth” and “belief” mean? That sounds like an ivory-tower philosophical puzzle. Most such questions can’t be answered, and “correct” answers, if they existed, wouldn’t make any practical difference. However, wrong ideas about “truth” and “belief” have large practical consequences, so getting a better understanding is important.
Believing true things matters. “HIV is the cause of AIDS” is true, and figuring that out has saved tens of millions of lives. Some politicians, religious leaders, and “alternative medicine” advocates said they “didn’t believe” HIV is the cause of AIDS. On that basis, they blocked HIV prevention and treatment, causing hundreds of thousands of horrible, unnecessary deaths.
We’ll find that the sense in which “HIV is the cause of AIDS” is true is more complex, fascinating, strange, and consequential than you’d probably think. I’ll explain the relevant biology in detail—and I suspect you will be surprised! There are practical medical and public health consequences to this unexpected sense.
“Epistemology” means ways of working with truth, belief, and knowledge. In the material world, there are only sort-of truths. Due to pervasive nebulosity, there are very few absolute truths, if any. Meta-rational epistemology provides a toolkit for working with sort-of truths, beliefs, and knowledge.
This post is a case study in meta-rational epistemology.
“HIV is the cause of AIDS” is true in some sense. Which sense? What sort of truth is that?
“HIV is the cause of AIDS” is not a subjective opinion. We can be almost perfectly certain it is true, on the basis of overwhelming factual evidence, with no meaningful room for doubt.
However, it’s also not objectively true, intrinsically true, or absolutely true. It’s true only relative to particular situations and purposes. It’s true only “in some senses.” We’ll see that it’s scientifically uncontroversial that, for some critically important purposes, other things are the cause of AIDS.
The discovery that HIV is the cause of AIDS was a scientific triumph. That relied extensively on rational methods. Still, the fact itself lacks many distinguishing aspects of rationality: objectivity, precision, generality, abstraction, and conformity with formal logic. Meta-rationality was critically necessary during the discovery, and for understanding now specifically what “HIV is the cause of AIDS” means.
The same is true of all scientific knowledge, to varying degrees. This post provides examples of how that works in practice.
The first two sections explain how “HIV” and “AIDS” are purpose-laden, contextual categories, not objective ones. (This will surprise you!) Whether something counts as HIV or AIDS is ultimately a matter of functional resemblance. It is therefore a meta-rational judgement, not something that can be decided rationally and objectively. These sections also explain why the categories have to be defined in terms of each other.
The most important word in “HIV is the cause of AIDS” is cause. What does that mean? This may seem obvious, but it’s not. Philosophers have tried to explain, and totally failed. Scientists generally assume (without thinking about it) that they understand causality, but they don’t.
Much of the post explains a meta-rational understanding of causality. “Cause” is not one thing, but a diffuse collection of nebulous thought-forms, causal schemas.
Selecting which sort of rationality to apply, for particular purposes in particular contexts, is a key meta-rational skill. In this case, different causal schemas explain different aspects of HIV/AIDS biology. Overall these add up to the “cause” in the overall sense of “HIV is the cause of AIDS.”
To understand how “HIV is the cause of AIDS” is true, one must know a bit how HIV does cause AIDS. Reading this, you will learn about biological mechanisms I find surprising and fascinating! I hope you do too.
(High school biology is enough background to understand all the main text. I’ve put some more technical material in footnotes.)
A final section points out explicitly how the scientific details we covered provide concrete examples of key meta-rational themes.