must | must to

Modal verbs are never followed by to, except ought to:

• I must go now. [obligation]
• We should sell the company cars. [desirable]
• I will arrive at 11.
• We ought to order our food now.

This rule does not apply to those words or phrases which act like model verbs:

• We are able to come to the meeting.
• We can come to the meeting.

Ought to is formal and you can use must [obligation, duty or correctness] or should [desirable] instead:

• I ought to go now. [obligation]
• We ought to sell the company cars. [desirable]

Our online courses and modules are designed with you in mind:

• flexible: you have busy lives, so our courses fit your schedule
• practical: we use everyday examples and situations to help you understand
• practice: there is only one way to improve; mistakes are there to help us learn
  
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Our online module How to avoid common mistakes takes you through the most common mistakes and how to avoid them:

How to avoid common mistakes