Changing the game doesn't necessarily mean you will win it. Prohibiting nuclear weapons won't automatically lead to disarmament. So once a ban treaty is in force, what happens next?

A ban treaty provides the two missing elements necessary for nuclear disarmament: a beginning and an end - a solid legal base and a well-defined objective.

There may be many different paths, steps and measures to link the beginning to the end: reductions, de-alerting, negative security assurances, fissile material controls - all the usual worthy ideas trotted out earnestly, endlessly and pointlessly in the CD, NPT, OEWG and elsewhere, as well as new ones.

A ban treaty anchors all these measures on a firm base - nuclear weapons are illegal - and locks them into a clear objective - total nuclear disarmament.

A ban treaty provides a collective international platform to discuss, develop, pursue and enact these measures - a platform that is under the control of states unequivocally committed to nuclear disarmament, and fully open to civil society.

The treaty will concentrate and focus all nuclear disarmament activity, re-energize civil society campaigns, and magnify the pressure on nuclear-armed governments from within and without.

A ban treaty provides a better home for non-proliferation and nuclear security work, free of the inherent flaws of the NPT. Those outside the ban treaty, but with a strong interest in non-proliferation and nuclear security, will find themselves obliged to engage with the ban treaty membership.

A ban treaty frees the non-nuclear-weapon states from the need to preserve harmony and consensus in the NPT at the expense of disarmament. The parties to the ban treaty will make their own collective assessment of the progress of nuclear-armed states towards disarmament. The parties will take the steps they consider necessary to encourage progress. They will hold the nuclear-armed states accountable.

In short, the parties to the ban treaty will be in control:

• They will take responsibility for advancing nuclear disarmament.
• They will act, not wait.
• They will start to build a world that eventually the nuclear-armed states will want to join.

This is the challenge, and victory is far from guaranteed.

But you can't win if you don't play.