Tortured, Restless Souls

Moored Kingscote, Kangaroo Island
Wind: South, F3 gentle breeze
Weather: overcast, mild
 
I have had a quiet and relaxing day today.  I caught up on some sleep, then, in the afternoon, cleaned out the lazarette. I was looking for that clicking sound from the windvane self-steering and thought it might have been coming from a loose bolt which tightens up from inside the lazarette. But the suspect bolt was tight as a drum, so I will have to look elsewhere for my mystery click.
 
This evening I have been studying a bit of philosophy – Critical Thinking 130, stuff about necessary and sufficient conditions. The exercises are a bit like grammar parsing exercises. For anyone interested here are a couple of examples (I wonder what the tutor would say):
 
For each of the following sentences:
(1) state the necessary and sufficient conditions
(2) paraphrase the sentence, to get an equivalent sentence which uses all instead of only , or only instead of all, and
(3) give an example of something that, if it existed, would be a counterexample to the sentence.
 
 
(i) Only dogs are hairy.
    1.  Being a dog is a necessary condition for being hairy, being hairy is a sufficient condition for being a dog.
    2.  All hairy things are dogs
    3.  Unicorns are hairy, unicorns are not dogs, therefore not only dogs are hairy.
 
(ii) All soap sales executives keep jaguars as pets.
 
    1.  Being an entity which keeps jaguars as pets is a necessary condition for being a soap sales executive, being a soap sales executives is sufficient to be an entity which keep jaguars as pets .
    2.  Only entities which keep jaguars as pets are soap sales executives.
    3.  My girlfriend (if she existed) is a soap sales executive, and she keeps unicorns - not a jaguar in sight, therefore … though there is that deep purring under the bed at night. Maybe its true!
 
(vi) Every rose has its thorns. [All roses have their thorns]
 
    1.  Being a rose is a sufficient condition for having thorns.  Having thorns is necessary for being a rose.
    2.  Only things with thorns are roses.
    3.  The midnight unicorn rose is a rose without even a single thorn, which seems a bit ironic really.
 
(ix) All poets are tortured, restless souls.
 
    1.  Being a poet is sufficient for being a tortured restless soul. Being a tortured, restless soul is necessary for being a poet.
    2.  Only tortured, restless souls are poets.
    3.  Gee, I can't think of a single poet who is, or was not, a tortured, restless soul. There was this soap sales executive who dabbled in poetry, you know, my girlfriend, the one who keeps unicorns, and she is anything but tortured and restless. Mind you, she should be, but you know soap sales executives, and she does keep unicorns after all. I guess dabbling in poetry, and bad poetry at that, mostly about clean unicorns – something Freudian to do with the horn I am sure, hardly puts one in the category of being a poet.
 
(x) Every dog will have its day.  [All dogs will have their day.]
 
    1.  Being a dog is a sufficient condition for being an entity which has its day. Being an entity which has its day is a necessary condition for being a dog.
    2.  Only an entity which has its day is a dog
    3.  Unicorn was my dog (girlfriend thing). He was de-sexed from puppyhood. He never had his day.
 
I am not sure I am really cut out for this philosophy stuff after all.
 
Nonetheless, All is well . . . or is that, Only well is all?