We formulate ten questions, covering outstanding aspects of thephenomenology of glassforming liquids, which we believe must beproperly answered by any successful theory of structuralglassformers. The questions range across thermodynamic, masstransport and vibrational dynamics phenomena. While thesequestions will only be addressed properly by a collectivevariables approach (many aspects of which are reported in theseproceedings) a number of them can be dealt with by use of simplephysical models of appropriate form. Here we discuss one suchmodel in which the existence of elementary configurationalexcitations of the amorphous quasilattice is proposed. Thesestates, which may range from broken bonds to packing defects,can be excited independently in the majority of cases, orcooperatively in others. We summarize essential results of thismodel. These suggest that the source of the different fragilitiesin liquids (and the reason that structural glasses, alone among`glassy' systems, have marked heat capacity jumps at Tg) maylie largely in the way these configurational excitations couple tothe vibrational modes of the system. The generation of lowfrequency modes in the density of vibrational states, as a directconsequence of the excitation of configurational states,explains why the quasi-elastic scattering from fragile liquids isso much stronger near and above Tg than in the case of strongliquids, and why the normal glass transition can be detected inpicosecond time scale experiments.Interactions among the `excitations', or `defects', are taken intoaccount using the one component system equivalent of the binarysystem `regular solution' model (which keeps only the first orderterm of the free energy of mixing expansion). We show that aliquid-liquid first order transition must occur at sufficientlystrong defect-defect interactions. The highly overconstrainedamorphous silicon quasilattice is a strong candidate for such atransition. We identify the `first order melting' of amorphoussilicon, and the sudden, reproducible, termination of supercoolingin experimental liquid silicon and germanium, with the phasetransition predicted by the model. Many more cases of this phasetransition may be anticipated, and a corresponding range ofglasses with low residual entropies - approaching the `perfect'glass state - are predicted.