A musing contributed by my friend Cliff:
This sentence is very often heard, in political discussions, and in any discussions where there is a strong disagreement: “You don’t know what you are talking about!” Very rarely, quasi never, would you ever hear someone saying, “I don’t know what I am talking about.” Consider that this expression is almost universally misused. What is really meant when someone says this is, “You have the wrong information.”, or “You have little or no information on the subject.”, or, “You have reached a conclusion whose error should be obvious.”
Let us illustrate with an example. Suppose someone says, “I think that the moon is made out of green cheese.” That person probably does, in fact, know what he is talking about. He knows what the moon is, what green cheese is, and he knows he is talking about the composition of the moon – and so, most probably, does any person he happens to be saying this to. Therefore they both know what they are taking about, that is, the composition of the moon, whether it is green cheese or not. Most of us would consider this as being incorrect, being based on wrong information or conclusions, but the subject matter and its various parameters are clear to all parties concerned.
So what then might be a legitimate use for this expression, “not knowing what you are talking about”? We could start by re-phrasing it as, “we actually don’t know what is being talked about.” Where this happens is when for the parties involved in a conversation, or even a person alone, their definitions and assumptions that are not clear, or not common to the persons involved. Let us use an example, of the current fad among the “woke” that there are 130 sexes. (Germany is much more conservative, in both senses of the word, with only 30+ sexes) The best approach to find out whether such a person “knows what he (or she/”they”) is talking about,” is to ask an incisive question, such as, “Do you mean sexes, or do you mean sexualities?” A bit of elaboration might go along with the question: “Heterosexuality is a sexuality, as implied by the word -sexuality- in the word hetero-sexuality.” Same is true for homosexuality, bi-sexuality, trans-sexuality, etc. In Wikipedia we have this article: https://en.wikipedia.org/wiki/List_of_gender_identities . Looking through this list, we see various combinations of male and female, such as a male wanting to be a female, vice-versa, being neither male nor female, being in-between, etc., but no clear statement of what a third sex might be. An interesting comparison is to another “woke” website, listing various sexualities: https://orientation.fandom.com/wiki/List_of_Sexualities . As inscrutable as many of the labels on this website are, at least they are clear that they are talking about sexualities and not sexes. (As an aside, here is some advice to Jr. High and High School students who may face expulsion for uttering the forbidden statement, “There are only two sexes.” Just ask, “excuse me, do you mean sexes, or do you mean sexualities?” And see where the conversation goes from there.)
All of this is a long-winded example to distinguish what it means to “know what one is talking about”. The principle is the same as Euclid laid out for his geometry, some 2,300 years ago. One starts with definitions, then proceeds to assumptions (also called first, or originating) premises, and then one can follow a set of consistent sequential steps that lead to reliable conclusions. Then, although we may disagree on the conclusions, i.e., the steps that lead to those conclusions, all parties involved at least know what they are talking about.
We can see where this is missing for instance in Senate and Congressional committee hearings. For instance, when Senator Rand Paul asks Dr. Fauci about financing gain-of-function research Fauci replies that he has never engaged in financing gain-of-function research. He is, in a sense, telling the truth, because he is using a different definition of gain-of-function than was used before the pandemic, and the senator is still using the old one. In this case, ironically, Dr. Fauci knows what he is talking about, but Senator Paul does not.