[Ed Swaine is Professor of Law at George Washington University Law School]
Larry Helfer is the perfect author for a chapter on the topic of treaty flexibility mechanisms: he writes from both theoretical and empirical perspectives, has a wide range of substantive expertise (including in human rights and trade, two fields that are central to this topic), and has a penetrating and remarkably clear style of analysis.  He deliberately provokes a number of questions in his chapter and post; because I’m conscious that blog readers themselves have numerous “exit” options, like closing this tab, I will try to be brief and touch on only a few.
This topic includes a wide variety of behaviors – reservations, denunciations, suspension, differentiated treatment, amendment, withdrawal, and so forth – and one set of issues concerns nomenclature and taxonomy.  Larry has a state-of-the-art table in his chapter laying out and sorting the flexibility options.  Personally, I have never been happy with describing certain formal flexibility mechanisms (those involving temporary relief from treaty obligations) as “escape” clauses, supposedly as distinct from “exit” clauses that entail permanent cessation of status as a treaty party.  Prisoners do not “escape” from Alcatraz with a view to returning; a word like “avoidance” better captures the idea in this context.  More generally, the categorization of flexibility mechanisms has certain routine difficulties – the basic problem of trying simultaneously to sort on 
when a state seeks flexibility and 
what its legal consequences are; conflicting tendencies both to include and exclude certain noncompliance acts as informal flexibility mechanisms; and an inherently unsatisfying distinction between so-called unilateral mechanisms (not always exploited in a completely autonomous fashion) and collective mechanisms (frequently, one suspects, prone to exploitation or capture by particular states).  Typology is rarely gripping, and I don’t want to mislead anyone into thinking that Larry’s chapter is focused on these questions or has unique difficulties with them.  However, they matter because we are concerned with the relationship among these mechanisms, principally in order to describe the choices states confront and make; he highlights this in his post as well.  In addition, beyond worrying whether these descriptions have formal integrity, we should also try to explore whether these are in fact the way state representatives think about the alternatives.  It might be the case, for example, that they focus predominately on collective rather than unilateral forms of flexibility, or informal rather than formal avenues, either of which might marginalize other kinds of inquiries.
A second set of issues concerns the proper perspective on these questions.