They are always written, because by writing down a Constitution you 'fix' its provisions. After that, a Constitution always is very hard to change or make Amendments to. And that makes it rigid.
A constitution by it's very nature is a foundation for government so it has to be written. There has to be a means to solve problems, run the government, and to know what is right or wrong. The framework is the limits of the boundaries set for the government and if it wasn't written down when problems arise people would have to guess what the rules are. When teams play a game they have to know the rules and it is the same for government.
Edward Washington Suppiger has written: 'An analysis of the motion of a rigid body' -- subject(s): Dynamics, Rigid, Rigid Dynamics
Jens Wittenburg has written: 'Dynamics of multibody systems' -- subject(s): Rigid Dynamics 'Dynamics of systems of rigid bodies' -- subject(s): Rigid Dynamics
John Prescott has written: 'Mechanics of particles and rigid bodies, by John Prescott' -- subject(s): Dynamics of a particle, Dynamics, Rigid, Mechanics, Rigid Dynamics
Itself
written and unwritten, codified and uncodified flexible and rigid
Vladimir Kitaev has written: 'Rigid rod polymers in confined geometries'
S.W Ekanayake has written: 'Rigid and pin jointed plane frame analysis'
James R. Pounder has written: 'On relativistically rigid surfaces of revolution'
W J. Louden has written: 'An elementary Treatise on Rigid Dynamics'
Joannes Terheijden has written: 'Syntheses and structural aspects of rigid arylplatinum complexes'
J. R. Pounder has written: 'On relativistically rigid surfaces of revolution'
Dietrich Koch has written: 'Characterisation of the regeneration performance of rigid ceramic filters'