Valid and Weak Forms of Arguments Using Conditionals

So one thing in Chapter 6 that I read was about valid and weak forms of arguments using conditionals.  In this section of the chapter, Epstein discusses how an argument can be valid, but it can also be weak at the same time.  A direct way of reasoning with conditionals would be: If A, then B, A, Therefore B.  However, an indirect way of reasoning with conditionals would be: If A, then B, not B, Therefore not A.  These structures are seen to be valid forms of arguments, however, there are valid forms that would be considered weak arguments, such as: If A, then B, B, Therefore A  and If A, then B, not A, Therefore not B.  
An example of a weak yet valid argument would be:
If Sally goes shopping, then Hank gets mad.
Hank is mad
Therefore, Sally went shopping


This is valid because when Sally shops Hank gets mad.  However, it is weak because even though Hank is mad, it doesn't necessarily mean that Sally went shopping because that isn't the only reason why Hank ever gets mad.  He could be mad because of another reason.