The argument "just because you read it on the Internet, doesn't mean it's true" is not an argument. It's a statement. It's may even be a factualy statement, but it does nothing to dismiss the original argument.
Sure lots on the Internet is dodgy. But there are good sources, and merely claiming the fact it's on the Internet makes the source unreliable is a poor argument. Actually it's not an argument, it's merely a way of dismissing someone else's claim. It sounds strong, but it's pretty weak way to attempt to disprove or discredit someone else's statement. If you can't dismiss my statement with a counter argument or a alternative source of information, then you can't discredit my source either.
I'm sure it's a fallacy but I can't tell which one. [UPDATE - It's Argument from fallacy, thanks Fer.]
This is what "you can't believe everything you read" has evolved to.
1. Matthew
The thing about Wikipedia is that anyone can stick up an explanation for something that isn’t defined. So it may or may not be true.
I prefer the Uncyclopedia, as I know everything I read there is total bollocks.
2. Fer
The fallacy involved is “Argument from fallacy”.
That is, the view that because your argument is fallacious (because it is an Appeal to Authority) then your conclusion must be false.
And to prove I’m right I refer you to the relevant Wikipedia articles:
Argument from fallacy and Appeal to authority
3. Adrian
Ah thanks Fer. I found Appeal to authority but I couldn’t find the counter to that.
Argument from fallacy is exactly what I was looking for.
4. Fer
The great thing about the “argument from fallacy” article is that the “obvious truthhood (sic)” that they give as an example is actually false.
Which just goes to prove that “just because you read it on the Internet, doesn’t mean it’s true”
5. Adrian
What in the example is false? I see a possible mistake in the way they have given acceleration, although it depends on how you see the way they have used the word rate.
However being the Wikipedia if you see a problem, you can just correct it.
6. Fer
First the obvious errors: 1. It says that it falls “at a rate of..” - it doesn’t fall at a constant rate, it falls at an increasing rate, starting at zero and with an acceleration (which might be 9.80655). 2. g is not 9.80665 meters per second, it is 9.0665 metres per second squared.
Next, the other errors - these are errors in the statement which under normal circumstances one would ignore, but since this is stated to be an example of an “obvious” truth i.e. one whose truth is unassailable - accordingly it is justified to be slightly pedantic. 3. g is only approximately 9.86055 m/s^2. 4. The statement ignores air resistance. 5. The statement ignores the fact that g varies depending on where you are relative to the earth.
We’ve already covered much of this on Dan’s blog - let’s not go any further.
As to amending Wikipedia, (a) I can’t be bothered, and (b) I think it’s amusing and harmless to leave it as it is.
7. Adrian
Well the word ‘rate’ implies change. The only constant change or constant rate, is the acceleration. At some far reaching push you could probably massage the semantics into making it look accurate. But I think they just forgot the extra “per second”.
As for being pedantic, maybe it’s a poor choice of example then because going into that sort of detail would confuse the simple explanation which is about fallacies, not about physics.
I still think you should amend at least the non pedantic part of your comment on the W’pedia.
8. Fer
Why, what’s stopping you? You could also add the example from your original post.
9. Fer
Another point is that even if they corrected those errors, the original argument “When I let go of this pencil, Angels from Heaven on high will push it downward. Therefore, it will fall…” is not a logical fallacy.
(It might be an incorrect explanation of the phenomenon of falling, being based on a false premise - one could never prove either way - but that doesn’t make it logically fallacious.)
The further examples given (and yours) are much better examples.
10. Julius
I think there are (at least) two fallacies here.
First, this looks like a straw man fallacy to me. I’m sure nobody in their right mind would suggest that the existence of piece of information on the Internet “means it is true”, so the comment it an implied attack on a position nobody holds. (Their statement is obviously true, but it it equally obviously irrelevant to the truth or falsity of the specific information you were discussing).
Secondly, their implied position is something like:
The set S contains objects which are individually either of type A or type B. X is a member of S. Therefore X is of type B.
If I had to give this one a name, it might be “Argument from Stupidity”. :-)
Actually, looking at Wikipedia, it’s probably the Fallacy of Composition:
A fallacy of composition arises when one infers that something is true of the whole from the fact that it is true of some part of the whole.
This would only fail as an analysis if there were no true statements at all on the Internet, but then you would probably already be aware of that and the conversation would never have happened.