The simple statement is that the frequency difference between the lines in a resonance reflect the true coupling constant only if all the frequencies of the components of the spin system giving the resonance follow the first-order condition of the resonance frequencies being much larger than the coupling constants involved. In all other instances, which in practice is actually the majority, the difference in the frequencies between lines is not the true coupling constant as second-or higher-order effects take place. Already in second order spectra, not only is the coupling constant not equal to the line frequency difference, but the chemical shift is not the center of the lines. These considerations do not only apply to multiplets, but to many signals that appear to be of relatively simple multiplicity (t, dd, ddd, etc.).