Many to many relationship with note field for each relation

I'm trying to create a many to many relationship while storing some information about that particular relation. For example:

A SurveyQuestion has many AuthoritativeSources. When an authoritative source is chosen for a question, the rationale (or justification) for the selection should be documented in a note.

An AuthoritativeSource can be used in many SurveyQuestions.

In a database this would be represented as:

SurveyQuestion >-< AuthoritativeSource

SurveyQuestion

- ID

- QuestionText

AuthoritativeSource

- ID

- Name

SurveyQuestion_AuthoritativeSource

- SurveyQuestionID

- AuthoritativeSourceID

- Rationale (Single line field)

I can create a multi-select list box in the SurveyQuestion to represent the relationship but where do I put the rationale for the selection?

We want to create two reports:

1. Each survey question with its authoritative source and the reason why that source makes sense (rationale).

2. The questions that refer to a particular authoritative source with the rationale.