Fletcher, Neville H.2015-10-182015-10-180002-9505http://hdl.handle.net/1885/15952In molecular spectroscopy, an anharmonic oscillator has a nonparabolic potential which results in a nonharmonic absorptionspectrum, but the same oscillator treated classically has a precisely harmonic vibrational spectrum. To avoid confusion, it is suggested that such an oscillator should simply be called nonlinear. The term “inharmonic” is suggested as an appropriate descriptor for classical oscillators, such as metal bars, that have nonharmonic vibrational spectra even in the linear limit of small vibrations.© 2002 American Association of Physics Teachers. Publisher permission to archive the version was granted via email on 19/11/2015. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in American Journal of Physics and may be found at https://doi.org/10.1119/1.1509419200210.1119/1.15094192015-12-12