Take graded Lagrangians $(L_{1},\theta_{1})$ and $(L_{2},\theta_{2})$, hamiltonian isotoped to intersect cleanly, and such that the graded (relative) Lagrangian connect sums $(L_{1}\#L_{2},\theta_{1}\#\theta_{2})$ exist as above. Then a Lagrangian $L$ of Maslov class zero is said to be destabilised by the $L_{i}$ if it is hamiltonian isotopic to such an $L_{1}\#L_{2}$, and the phases (real numbers, induced by the gradings) satisfy

$$\phi(L_{1})\geq\phi(L_{2}).$$

If $L$ is not destabilised by any such $L_{i}$ then it is called stable.