Traditional solid-state synthetic methods take advantage of global stability through a direct reaction of components under equilibrium conditions that favour thermodynamically stable products. However, global stability is not a necessary condition for a material to be synthesised. There are alternative soft chemical methods such as sol-gel synthesis and chemical vapour deposition that provide low temperature processing routes to isolate metastable phases. One notable example is the formation of previously unknown metastable metal nitride semiconductors from high-energy precusors. While the space of hypothetical materials is infinite, a subset can be defined as locally stable following the criteria previously discussed. We posit that if a material is locally stable, there is a non-zero probability of it being synthesised by a motivated expert-with the caveat indicated in Fig. that phases with a higher energy than a competing amorphous phase are unlikely to be kinetically stable. A synthetic chemist is aided by the diversity of possible synthetic strategies, which can include extreme conditions (e.g. high pressure ), non-equilibrium approaches (e.g. plasma-electrochemical methods ), or even nuclear transmutation (e.g. Zn to Cu decay 76 ). Figure illustrates this suggestion. Note how both local and global stability must be evaluated at the relevant thermodynamic conditions. Synthesis of metastable crystals can be guided by the free energy methods described above. Traditional equilibrium pressure-temperature methods give access to the global stability and can identify ground state phases at selected synthesis conditions. If these phases are locally stable at ambient conditions, they have the potential to be quenched and persist outside of the synthesis environment where they are no longer the lowest energy phase.