This is from The IBM Style Guide: Conventions for Writers and Editors:
Then is not a coordinating conjunction. You cannot join independent clauses with then unless you add a semicolon or a coordinating conjunction.
- Click Start then select a program.
- Click Start, then select a program.
- Click Start; then select a program.
- Click Start and then select a program
Note that “then” is not a coordinating conjunction (such as “and,” “or,” and “but”). Using “then” as a coordinating conjunction creates a run-on sentence, as in the following example: “Do this, then do that.”
In my work as a technical-writer-in-free-time, I often have to write instructions like this one:
- Here goes the 1st step.
- Here goes the 2nd step.
- Open the preferences window, select the Paths tab, and note that the path in the File name field is missing.
Does it mean that the 3rd step in my instruction violates the IBM recommendations? I mean, it is essentially the same as
Open the preferences window, then select the Paths tab, and then note that the path in the File name field is missing.
The first then seems to violate the IBM guidelines, isn't it? Is it really a good idea to replace the first comma there with a semicolon?
Open the preferences window; select the Paths tab and note that the path in the File name field is missing.