What are the common issues of a class action?

In explaining how the common issues relate to the proposed members of the class, the defendants do not refer to evidence supporting their general assertion but do state as follows: In Walls v. Bayer Inc., supra, the court stated at Paragraph 44 that: “Section 4(c) of the Act requires that the claims of the class members raise a common issue, whether or not the common issue predominates over issues affecting only individual members.” The court went on further to say: “Section 4(c) requires that the action raise common issues of fact or law. It need not be determinative of liability nor dominant issues in the litigation. But they must be issues common to all members of the class in the sense that their decision at a common issues trial will advance the litigation in some meaningful way. Are the common issues ones that will have to be decided in respect of the claim of every member of the class, and will their being decided in a representative action avoid duplication of the fact-finding or legal analysis?”