Couldn't/Could Not

The difference in meaning between could not and its contraction just dawned on me:

The meaning of Hank could not eat the steak is ambiguous, but the meaning is clarified in Hank couldn't eat the steak. The likely meaning of the former sentence is that Hank was unable to eat the steak, as from being too full or out of time, but it could mean that recovering beef-addict Hank managed not to eat the steak that was placed before him and therefore is showing great signs of progress. The latter sentence can only mean the former explanation.

In summary, negatives are funny things, and great examples of why infinitive splitting is perfectly acceptable: Make sure not to turn right at Albuquerque lacks the definitive admonition of Make sure to not turn right at Albuquerque. If some grammar prude, in the middle of New Mexico, says to me that former sentence, I'm taking it easy which way or whether I turn.