Old rules versus current doctrine
Some of your historical style systems used hard caps such as 20 words per sentence and three sentences per paragraph. Those rules can be useful diagnostics for bloated writing, but they are too rigid to remain universal standards.
Your later work moved toward a better principle: many explanatory sentences read comfortably around 20–30 words, but meaning governs length.
A 12-word sentence can be confusing. A 35-word sentence can be clear if it contains one thought whose conditions belong together.
One thought per sentence is a default, not a law
Split when the reader must hold multiple independent claims at once.
Keep the sentence together when separating it would hide the relationship among cause, condition, and consequence.
Rhythm comes from expectation and variation
Your Aristotle reference translates rhythm into several prose practices:
- Vary sentence length.
- Use parallel syntax for genuinely parallel ideas.
- Break the pattern when the argument turns.
- Use a short sentence to land a recognition.
- Place consequential information where it receives stress.
- Vary paragraph length with pace and reasoning density.
- Read aloud.
The short sentence works because it contrasts with what surrounds it. If every sentence is short, none receives special force.
To place a point where it receives stress, see Module 13: topic position and stress position.
Read aloud for syntax, not performance
Reading aloud exposes:
- hidden repetition
- overloaded clauses
- missing words
- false rhythm
- places where punctuation fights natural phrasing
- lines that sound written rather than thought
Do not edit toward a theatrical voice. Use your ear as another parsing system.
Make syntax follow the thought
The Marks study gives a better standard than sentence length. A sentence is easy to follow when its grammar mirrors the relationship among the ideas.
If the thought is causal, make the causal relation visible. If it is conditional, keep the condition attached to what it governs. If it is a contrast, let the syntax turn where the reasoning turns.
A long sentence can remain clear when it resolves one relationship before introducing the next. A short sentence can remain confusing when it hides which fact causes, qualifies, or contradicts another.
When editing a difficult sentence, do not begin by counting words. First draw the thought:
X → because Y → unless Z → therefore A
Then make the sentence expose that structure.