"A manual written to help students to understand the module"

Question

Or should it be without the second "to" like this: "A manual written to help students understand the module"? I'm guessing that either is generally acceptable but is there a traditional grammar rule about this? Thanks

Answer 1

The Cambridge Dictionary suggests that you can use the infinitive with or without to:

Jack is helping me to tidy my CDs. or Jack is helping me tidy my CDs.

When "understand" lacks a to but functions as an infinitive, it is called a bare infinitive. These bare infinitives are sometimes interchangeable with to-infinitives, depending on the verb. "To help" is one such verb.

So the only difference is which one you like better for other reasons, like personal preference.