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Comment by Garbage | Hacker News Reader

"If quantity of app titles were all that mattered, we’d all be using Windows, not Mac OS X, right?"

Err... Wait, are we all using Mac OS X?

His logic is sound, but you're misreading him: he's saying that (quantity of app titles all that matters) => (we're all using windows). We're not all using windows, so by contradiction quantity of apps is not all that matters. He's not saying that everybody is using OS X, just that not everybody is using windows.

Exactly. This is a logical error that I keep seeing being made from people, and having a logics background I can't help to notice.

A implies B does not imply that not B implies not A.

Actually, (A implies B) does imply (!B implies !A). It's the contrapositive.

For example, from Wikipedia, "All birds are animals" does imply "All non-animals are non-birds". http://en.wikipedia.org/wiki/Contraposition

Apparently he meant "(A implies B) does not imply (B implies A)". Affirming the consequent and all that.

>A implies B does not imply that not B implies not A.

Wait, what?

Every time I eat a hard candy, I get a toothache. I don't have a toothache, therefore I didn't eat a hard candy.

Actually I made a mistake there. Going on mere memory and without checking, I put the double negation, which comes from an axiom.

So yes, what I meant is "If I eat hard candy, I get toothache" does not imply "I have a toothache, so I ate hard candies". Which is the form I was commenting on. I should have provided an example (and double checked!).

Actually, it does mean that.

If you write out the truth table, A -> B is equivalent to ~A \/ B, which means ~B -> ~A. This is called the contrapositive and is a valid inference. The two classical invalid inferences from A -> B are ~A -> ~B (the inverse) and B -> A (the converse).

The audience he's been speaking to since August 2002 are.

If you confine your worldview to right-thinking people, yes.

There are savages outside of city walls, who breed via biological means and use (shudder) Windows. We try not to think about or discuss them in polite society.

Also, where are the killer games for OS X?

Killer apps exist.

They used to have them, most of them were made by Adobe.

"We are all" is not the same as "everybody is…" — it just means that everybody in some group that the speaker counts himself a part of shares the following attribute.

But even that is a stronger claim than Gruber made. He simply said that not everybody in the group he was talking about preferred Windows — a majority could even prefer Windows and his point (that the Mac's software selection appeals to some people even though it's unquestionably smaller) would stand.

In Gruber's world we are.

No, I think this is not correct. Most of the Gruber audience are, but he is of course well aware that OS X does not reach the two digits in market share.

EDIT: spelling.

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