Whether it's to start analyzing a detail or impressing someone in conversation, understanding a classical building begins with an awareness of the different classical orders of architecture. In the historical records of architecture, the first account of the orders was written by Vitruvius: "[...] The orders came to provide a range of architectural expressions, ranging from roughness and firmness to slenderness and delicacy. In true classical design, order choice is a vital issue—it is the choice of tone,"  which for the author, synthesizes the "architecture grammar." 
According to John Summerson, author of The Classical Language of Architecture, "[...] a classic building is one whose decorative elements derive directly or indirectly from the architectural vocabulary of the ancient world—the 'classical' world [...]. These elements are easily recognizable, such as, for example, the five standard types of columns that are used in a standardized way, the standard treatments of openings and pediments, or, still, the standardized series of ornaments that are employed in classical buildings."