In hmolscience, letter rhyming derivation method refers to the equation derivation method, commonly seen in economic thermodynamics, wherein theorists will attempt to derive a thermodynamic formula of a given subject or system, e.g. economics, sociology, anthropology, guided by the poetical model or idea of letter or word rhyme, e.g. “U” of utility (of economics) is the same letter as “U” of internal energy (of thermodynamics), therefore they must be the same, as defined by the first law (Hans Kreuzer, 2010); or “P” of price level (of money flow systems) is the same as “P” of pressure (in thermodynamics), therefore they must be the same, as defined by the ideal gas law (John Bryant, 2010). 
The letter rhyming derivation method is an example of what NOT to do, in that the method, and all results derived therefrom, has no logical basis.
The correct method is to go through thermodynamics proper to do the derivation, e.g. start with the works of Clausius, understand what a “system” is, understand what the “equivalence-value of all uncompensated transformations” means, understand the “mechanical equivalent of heat”, understand basic definitions, e.g. pressure, temperature, volume, mol, molecule, bond, energy, etc., and then do the derivation from the bottom up, going through the proper branch of thermodynamics, e.g. Edwin Wilson being taught thermodynamics by Willard Gibbs, the founder of chemical thermodynamics, who then told his student that the a good approach to formulate the thermodynamics of economic systems and equilibrium would be to start with Gibbs’ equation 133 and derive upward therefrom.
1. (a) Kreuzer, H.J. and Tamblyn, Isaac. (2010). Thermodynamics (§8.6: Athletes: the Human Engine, pgs. 160-62; §8.6: Thermodynamics in Economics, pgs. 162-66). World Scientific.
(b) Bryant, John. (2010). “A Thermodynamic Approach to Monetary Economics: a Revision: an Application to the UK Economy 1969-2006 and the USA Economy 1966-2006” (pdf), Vocat.co.uk, Feb.