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Give us a bone here? Can you give you an example of what you will call an Action and what you will call Next Actions?
Based on what I understand of GTD and your Question I am going to reply, I hope is useful.
A next action is the next step you need to do to move a process forward, an action is something you will need to take in some step of the process.
Let me give you an example:
Project: Travel to Brazil (yes it is an actual project in my list)
Get plane Tickets
Get Hotel Reservations
Get Meetings with Prospects and Costumers
All those are actions, they will need to happen at some point, but it is not the next action to move this project forward, so lets think about it for a moment.
Get the plane tickets or Hotel Reservation; ok I cannot do this until I have some idea what I going to do in Brazil and if I can have enough meetings to go; therefore are only ACTIONS
Lets see the other Item. Get Meetings with Prospects and Costumers. This is not a Next Action nor an Action, is more a subproject.
My Next action will be identify witch costumers I am going to visit in Brazil. Assuming that it is an obvious question then my next action will be Call Costumer X to program a meeting in Brazil.
That will be my next action: "Call Costumer X to program a meeting in Brazil."
In my case will be in my @Calls List and but I will track all those other actions in my project notes or folder (depending in the project) for future reference, for example:
Once confirmed the meeting my next action will be Buy ticket in AA to Brazil as well as Get Hotel Reservations in Brazil. (In my case both in my @Computer List, since this I need to do it online.