Jam yesterday and jam tomorrow but never jam today

[Anthony Appleyard]

I always thought that this expression in "Alice in Wonderland" was merely childish storybook stuff and nothing to do with anything learned. But recently I found on the Web that Lewis Carroll when writing "Alice in Wonderland" did not invent this expression, but took it from an old Latin grammar that used it as a rule to tell schoolboys learning Latin not to use "iam" for present events (for which instead use "nunc") but only for past and future events.

In the well-known "Ave Caesar, adsum iam forte" = "Hail Caesar, by chance I am here already", the tense seems to be present, but in the sentence, the speaker is already here, and so his arrival here was in the past.

[Barry Hofstetter]

Of course, there is an even closer connection to the classical world:

https://www.biography.com/people/lewis-carroll-9239598

Carroll loved to entertain children, and it was Alice, the daughter of Henry George Liddell, who can be credited with his pinnacle inspiration. Alice Liddell remembers spending many hours with Carroll, sitting on his couch while he told fantastic tales of dream worlds. During an afternoon picnic with Alice and her two sisters, Carroll told the first iteration of what would later become Alice's Adventures in Wonderland. When Alice arrived home, she exclaimed that he must write the story down for her.