Lafari@lemmy.world to No Stupid Questions@lemmy.world · 10 months agoIs "If A then B" equal to "B if and only if A"?message-squaremessage-square56fedilinkarrow-up135arrow-down18
arrow-up127arrow-down1message-squareIs "If A then B" equal to "B if and only if A"?Lafari@lemmy.world to No Stupid Questions@lemmy.world · 10 months agomessage-square56fedilink
minus-squareApepollo11@lemmy.worldlinkfedilinkarrow-up13arrow-down1·10 months agoYou’ve have some examples, but in case they are not clear enough: If [you have AIDS] then [you are unwell] [You are unwell] if and only if [you have AIDS] The first one is not the same as the second. Why? There are plenty of ways to be unwell, without necessary developing AIDS. The first statement only defines one possible path to B, not all of them.
minus-squareAmidFuror@kbin.sociallinkfedilinkarrow-up6·10 months agoNot just HIV, but full blown AIDS?
minus-squareBananaTrifleViolin@kbin.sociallinkfedilinkarrow-up7·edit-210 months agoActually a good example: If you have AIDs (A) then you have HIV (B). True You have HIV (B) if, and only if, you have AIDS (A). Not true If you don’t have HIV (B), then you don’t have AIDs (A). True, and the actual inverse of “If A then B”; which is “If not B, then not A”
minus-squareAmidFuror@kbin.sociallinkfedilinkarrow-up3·10 months agoIt’s important to stress the “full blown” modifier in any example.
You’ve have some examples, but in case they are not clear enough:
If [you have AIDS] then [you are unwell]
[You are unwell] if and only if [you have AIDS]
The first one is not the same as the second. Why? There are plenty of ways to be unwell, without necessary developing AIDS.
The first statement only defines one possible path to B, not all of them.
Not just HIV, but full blown AIDS?
Actually a good example:
It’s important to stress the “full blown” modifier in any example.