What is a Fact?

In general our dictionaries all suggest that a "fact" is something that has or can be shown to have happened: here are three such examples. The Oxford example includes an etymology, which I always find helpful in understanding the deeper meaning of a word.

Late 15th century from Latin factum, neuter past participle of facere ‘do’. The original sense was ‘an act’, later ‘a crime’, surviving in the phrase before (or after) the fact. The earliest of the current senses (‘truth, reality’) dates from the late 16th century.

Now when I was a boy in school, the way this was taught to us was as a distinction between "a fact" and "an opinion." A fact was said to be something that could be proven true or false. An opinion was a statement about reality which cannot be proven true, nor proven false. This model raised hackles among those who did not like the idea that a thing proven false was a sort of fact; it might be better to say that there is 'a fact of the matter' about it.

The ACLU gives us four "facts" about trans athletes today.

1) "Trans girls are girls." 

2) "Trans athletes do not have an unfair advantage in sports."

3) "Including trans athletes will benefit everyone."

4) "Trans people belong on the same team as other students."

Only one of those statements, the first one, is possibly a fact. The others all depend on things that fall in the category of opinions, e.g, "what does it mean to have an unfair advantage"? Obviously athletes do have advantages over each other, which is one of the reasons to have the competition: to see who is best. Many of these advantages are considered fair, for example, two boys who are differentially strong or skilled but of similar weight will be allowed to wrestle. That one boy has been wrestling for three years and the other one has never done it before is not considered an unfair advantage; it is for the unskilled boy to learn to do it better. That one is weaker will be met with the advice: "Grow stronger!"

So too for what it means for a thing to be a benefit, which we must know before we can evaluate (3); what it means to belong, etc. Those are value judgments that are opinions. One might say that 'to benefit' means to obtain some good, such as a scholarship; in that case, several people will benefit at the expense of several others, but it is not true that 'everyone' will benefit. Or one might say that 'to benefit' means to develop a character that accepts all kinds of others even when it is expensive to one's self; perhaps then 'everyone' will benefit, but not to the same degree -- some will have to pay a cost, and some will not. 

The first one is a fact, though, unless we turn 'being a girl' into an opinion. That actually seems to be the proposal: that if one feels like a girl, one is a girl. Yet there is a fact of the matter about this, which makes (1) a fact in the sense of being a false fact. This is not an opinion; and therefore, it is also not a prejudice (which is a 'pre-judgment') because no judgment is being made. We don't have to decide if an individual, X, is or is not a girl; we simply have to know that 'a girl' is 'a young female human being.' Whether X is or is not that depends on facts about X that we don't have to know to know that the definition of the word means that non-young human beings are excluded from the category, as are non-females, and non humans. There's nothing wrong with being a kitten or a foal, but they're not "girls" in a factual sense. If you call one "a little girl," you're speaking metaphorically, not factually.

And you are free to speak metaphorically! You're also free to speak falsely, as by saying that an opinion is a fact; or even to say that a fact ought to be an opinion. Freedom is important; but so is clarity of thought. One's freedom to say those things must not interfere with our ability to point out that, in fact, that is not how things are.