Ability and Inclination

My neighbor Jones will write no book,
Although he has a mind to;
Because, you see, he lacks the mind-
A fact he's grossly blind to.

My neighbor Brown will write no book,
Because he has no mind to;
Although he doubtless has the mind^___
A fact he's partly blind to.

One needs two things to write a book:
One needs to have a mind to,
And also needs to have the mind^___
Which facts let none be blind to.