I know this word, but I cannot think of it. It is driving me crazy. Example:
The murder rate in the National Parks is very low because the people who go to the National Parks are non-violent people.
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X is because of Y, when Y is simply a restatement of X.
"circular reasoning" or "begging the question" is one kind of logical fallcy. The most common example is "God exists because the Bible says so, and the Bible is the word of God". Another example, not so obvious, "Whatever is less dense than water will float, because such objects won't sink in water"
As @deadrat has mentioned in a comment, your sentence would be a good example of "circular reasoning" if you had written "The murder rate in the National Parks is very low because people who go to the National Parks aren't killed there very often."
- Circular reasoning (Latin: circulus in probando, "circle in proving"; also known as circular logic) is a logical fallacy in which the reasoner begins with what they are trying to end with. The components of a circular argument are often logically valid because if the premises are true, the conclusion must be true. Circular reasoning is not a formal logical fallacy but a pragmatic defect in an argument whereby the premises are just as much in need of proof or evidence as the conclusion, and as a consequence the argument fails to persuade. Other ways to express this are that there is no reason to accept the premises unless one already believes the conclusion, or that the premises provide no independent ground or evidence for the conclusion. Begging the question is closely related to circular reasoning, and in modern usage the two generally refer to the same thing. Circular reasoning is often of the form: "A is true because B is true; B is true because A is true." Circularity can be difficult to detect if it involves a longer chain of propositions. from Wikipedia
Perhaps a statement of the obvious or a truism.
It is a claim that is so obvious or self-evident as to be hardly worth mentioning.
hunger is often followed by a meal.
If a bacterial culture refuses to grow on the agar plate contained in that metalic mould, then the metal must be giving out something that stops the bacterial colony growing.
I offer as an Answer to my Question:
the statement has low explanatory power. Or, the statement has explanatory impotence.
Explanatory Power, from Wikipedia:
"Explanatory power is the ability of a hypothesis or theory to effectively explain the subject matter it pertains to. The opposite of explanatory power is explanatory impotence.
"In the past, various criteria or measures for explanatory power have been proposed. In particular, one hypothesis, theory or explanation can be said to have more explanatory power than another about the same subject matter
if more facts or observations are accounted for;
if it changes more "surprising facts" into "a matter of course" (following Peirce);
if more details of causal relations are provided, leading to a high accuracy and precision of the description;
if it offers greater predictive power, i.e., if it offers more details about what we should expect to see, and what we should not;
if it depends less on authorities and more on observations;
if it makes fewer assumptions;
if it is more falsifiable, i.e., more testable by observation or experiment (following Popper)."
I was fruitlessly searching my brain for "tautology", which Deadrat explained my example was not. I had actually estimated from data the murder and violent crime rates for the National Parks and was looking for an explanation of why they were so low. Nothing I came up with had much explanatory power; my explanations seemed like....what the heck is that word? Tautologies, which they were not. Centaurus and Graffito have given very good answers.