The phrase “I haven’t seen…” is an attempt to assert a
categorical negative claim. Let’s look at categoricals.
A categorical claim says that all X are Y.
If you can find even one example of X that is not Y, the
statement is false.
And since none of us are omniscient, nor can we access every
piece of evidence that might exist, we cannot make categorical claims – UNLESS
WE HAVE A COMPLETE DATASET.
To get a complete dataset to make claims about, we need a
clear definition of what is in our dataset and what is not. But we can make the
definition so stringent we defeat ourselves.
Real world example? You want to test a drug. If your dataset
of test subjects is strictly white males between 20 and 50, your results don’t necessarily
apply to women, to children, to the elderly, or to POC. So you can’t make the categorical statement that
“Drug X is 75% effective” except for test subjects who represent 10% or less of
the world’s demographics. But decades ago, everybody assumed that if it worked
on white males of a given age, it would work on everybody else. People died
over that assumption.
The “all X are Y” claim means every member of one dataset is
also a member of another dataset or has the same description. The problem comes
if you claim that all X are not Y. This can mean two things.
One is that no member of dataset X is in dataset Y or
matches the description in dataset Y. When we’re just talking normally, saying
“all X are not Y” could mean that some X ARE Y: “all dogs are not vicious” in
normal conversation could mean you’ve been talking about dogs that are vicious
but you want to point out that viciousness is not a universal quality of dogs.
That doesn’t work in logic. If you mean “some are not”, you
have to say “some are not”.
The other thing it can mean is that you are confusing inherent
qualities (essence) and qualities perceived or caused (accidence). This is the
basis for the “all dogs are not vicious”. The person saying that probably knows
that historically, abused animals turn mean. They’re saying that dogs are not
inherently vicious, the viciousness is caused.
Negation is an operation in Boolean algebra. It is a
categorical claim that something does not exist. When you don’t have a complete
dataset, making a negative claim risks somebody finding the exception that
proves your claim doesn’t hold water.
“I haven’t seen…” is an attempt to pretend that you have a
complete dataset. In reality, on social media for example, it only means that
you don’t follow every account on every possible platform.
Instead, it often means that you only follow the
accounts of people who already agree with you. It’s called “being in an echo
chamber”. If you want to say “I haven’t seen…”, make sure you do it inside your
echo chamber, because people outside it may have the evidence that what you say
is false. And so I have a habit of replying “follow more accounts”, especially
when I HAVE seen whatever the OP is denying.
Instead of saying “I haven’t seen…”, give the hard evidence
that the probability of existence is infinitesimal. Calculating an
infinitesimal probability of truth shows that an argument is “down in the
noise”, not worth troubling your head over. That’s what forensic DNA testing
does, tells the court that there’s an infinitesimal probability that somebody
other than the accused provided the sample that gave the test results.
Now. In logic, you can also defeat a negative by proving
that it creates an absurdity, reductio ad absurdam. It’s kind of like
what Elle did to her ex in class in Legally Blonde. He made a
categorical claim that a guy was not stalking the girl who birthed his child,
he was worried about what happened to the sperm he had donated. Elle reduced
that to an absurdity by asking if he would do the same thing if he donated to a
sperm bank or had a nocturnal emission. But that was in class, not in court.
So let’s be careful about both the categoricals and the negatives that we try to prove.
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