Although formulating the issue is simple in some cases, it can create confrontation and irreconcilable differences in others. The earlier the issue can be stated by the arbitrator, the easier it will be for all concerned. Regarding the handling of arbitrability disputes, the most common problem in the Federal sector is timeliness. Arbitrability questions should be raised early in the grievance procedure. They should not be of a frivolous nature and, if asserted, they should be established by persuasive evidence. 'Past practice' refers to a 'way of accomplishing something or a course of conduct, accepted by both sides, and which has as an asset some historical heritage.' To be enforceable or binding, a 'past practice' must meet certain criteria, such as the length, consistency, and disputants' acceptance of the practice. 'Past practice' is useful in explaining the intent of the parties, but it is only one of many tools and aids available to the advocates and arbitrators in their efforts to interpret and apply unclear or ambiguous language which the parties negotiated and placed in their agreement. Footnotes which contain references are supplied.