Greetings @owasco ,
Thank you for dropping by. ^__^
To answer your queries...the dictionary and antonyms are my consultants. We are what we think...we use our minds and our thoughts are expressed through the body sometimes but not necessarily always.
If one uses the word 'fit' with regard to the mind, one might be referring to good mental health, attention, problem-solving skills alertness, etc.
If we look at the antonym ..unfit, or the opposite of a 'fit mind' one might be described as a state of mental unfitness which could include conditions such as mental exhaustion, stress, anxiety, or depression.
And we can do the same for the word 'able' which is being used here as a synonym.
The analogy the philosopher was using of 'Grace' to the body was referring to the fact that we all can appreciate Grace expressed in a body...therefore the first part of the Principle...'What grace is to the body'...thus the title of the Photographs..'Ballerina'.....
Take the antonym of Grace....Awkward ....Not everyone is Graceful...however most can appreciate Grace when they see it....the philosopher knew the Greeks and Romans...they did appreciate Grace in the body....he was pointing out that ..What Grace is to the body....Good Sense is to the mind ....something that should be admired as well...and should be strived for.
Thank you for your kind words with regard to Artwork and the Roses.
Kind Regards,
Bleujay