Over the past several decades, a number of theories have been proposed that attempt to predict the temperature-dependent behaviour of disordered solids; however a clear consensus regarding the fundamental mechanism at or near the glass-transition temperature (T g ) has not yet been achieved . However, as originally proposed by Goldstein and expanded on by others, it has been suggested that the underlying shape and structure of the potential energy surface (PES) is responsible for dictating properties, including the dynamics, of glassy materials. Dielectric spectroscopy has become the standard technique for experimentally investigating the relaxational dynamics associated with the glass-transition, and such measurements have uncovered a number of characteristic relaxation fingerprints that occur within particular frequency windows, with the two most common being the primary α-relaxation (≈ 10 -6 -10 3 Hz), corresponding to entire-molecule rearrangement, and the secondary Johari-Goldstein (JG) β (≈ 10 -6 -10 9 Hz) relaxation, which has been suggested as a representing a special class of secondary relaxations strongly linked to the a number of physical properties . But while dielectric spectroscopy probes the (relatively low) frequency relaxation of electric-dipole vectors, numerous other techniques have been used to characterise the properties and glasstransition temperatures of glasses, including neutron scattering , Brillouin light scattering (BLS), dynamical mechanical analysis (DMA) , Raman scattering and, more recently, terahertz time-domain spectroscopy (THz-TDS) , amongst many others . In general, each of these methods were found to be sufficiently sensitive for detecting the α-and β -relaxation fingerprints, as well as the corresponding glass transitions (e.g. T gα and T gβ ), which are loosely defined as the slowing of the corresponding dielectric relaxation processes beyond time scales that are readily detected by experiment (≈ 100 s) . It is important to clarify that T gβ has only recently been explored in-depth, and it represents the vitrification of the β -relaxation process as originally described by Johari and Goldstein. There have been attempts to link the experimental observations at frequencies exceeding the dielectric relaxations (such as midinfrared, Raman or terahertz spectroscopies) to the fundamental process of collective translational and (hindered) rotational motions by means of a coupling process . However, given that most of these measurements probe processes that occur on drastically shorter timescales (femtoseconds to picoseconds probed in the infrared/terahertz vs. milliseconds to seconds for the relaxation processes associated with α-and β -relaxation) a more fundamental origin must exist that links the slow relaxation process with all the other experimental data. Given the importance of the PES on the properties of glasses, it is possible to explain the frequencyindependence of the relaxation processes as a manifestation of the PES structure. Importantly, we believe that it is critical to explicitly consider the molecular nature of the solids, their complete intra-and inter-molecular interactions, and the corresponding anharmonicity in their PES, particularly the inter-molecular anharmonicity (responsible for thermal expansion). While there exists a large body of work related to this topic, with a wide variety of theories having been proposed over the years, it is not surprising that this level of detail has not yet been achieved since such considerations are far from trivial to implement into theoretical models . However, this work will demonstrate how important both of these factors are for understanding the origins of glassy dynamics, and that previous oversimplifications might be the cause of certain discrepancies in the quantitative agreement between theory and experiment. This interpretation is aligned with the Coupling Model, which is based on the corresponding anharmonicity in intermolecular interactions, and helps to explain the origins of the intermolecular dynamics (inclusive of any cage-rattling motions) within the context of a PES picture.