Semicolon Between Long Dependent 'That' Clauses in a Series
The Semicolon
Rulebase Summary
When a sentence contains a series of dependent clauses each introduced by 'that,' use semicolons to separate them if the clauses are long (roughly ten-plus words each). If the 'that' clauses are short, commas are sufficient.
If there are only two 'that' clauses joined by a conjunction (and, but, or, nor), no punctuation is needed between them. If there are only two 'that' clauses with no conjunction, use a comma if they are short and simple, or a semicolon if they are long or contain internal commas. When the clauses are numerous or tabulated, semicolons help maintain clarity even if individual clauses are short.
Examples
Q. Doctor, assume that the patient had a prior history of cardiac disease, that he had been prescribed blood thinners for over two years, and that he stopped taking the medication three weeks before the incident.
Q. Doctor, assume that the patient had a prior history of cardiac disease; that he had been prescribed blood thinners for over two years; and that he stopped taking the medication three weeks before the incident.
Long 'that' clauses in a series are separated by semicolons.
A. He testified that the car was red, and she testified that the car was blue.
A. He testified that the car was red; and she testified that the car was blue.
Long parallel that-clauses — semicolon even with conjunction.
Style Guide References (1)
Morson's