What makes a short sentence short and a long sentence long? (And a long sentence a run-on sentence?)

1. That depends. (2 words)

2. That depends on a lot of things, including pacing (e.g., lengthy, dramatically slow sentences versus shorter, “faster” ones) and historical aptness (e.g., using longer sentences to make an eighteenth century fiction piece reflect that period’s slower pace of life); these elements should work together, allowing the reader to mentally “breathe.” (51 words)

The second sentence is about 25 times as long as the first and about 25 times more pompous, but is it the bane of seventh grade English teachers, the run-on sentence?

According to Merriam-Webster (https://www.merriam-webster.com/dictionary/run-on%20sentence), a run-on sentence is one containing two or more clauses not connected by the correct conjunction or punctuation. According to ThoughtCo (https://www.thoughtco.com/run-on-sentence-grammar-and-usage-1692069) there are five ways to fix (or put another way, avoid) a run-on sentence: (1) make the sentence into simpler, multiple sentences; (2) add semicolons; (3) add commas and joining words; (4) reduce spliced sentences into a single, cohesive sentence; and (5) place subordinating conjunctions before “fused” clauses.

The second sentence’s parenthetical phrases, commas and semicolon allow the reader to breathe. I will admit that changing the semicolon to a period and breaking the sentence into two sentences might be a better way to go, but it still just comes down to preference: I like long sentences, assuming they are coherent, don’t run on and don’t exhaust me. But are the long sentences I like too long, even if grammatically correct? Possibly. But which do you like better?

3. See Dick. See Jane. Dick and Jane see Spot. Spot is their dog. Spot sees a squirrel. The squirrel is fat.

4. Dick and Jane spied on their dog, Spot, who, in turn, spied on a fat squirrel.

I like sentences with meat on them. “Endomorphic” sentences. I vote #4.