 As mentioned above, when interference is suppressed in a two-slit experiment, the naive probability formula applies, and we can calculate the detection probabilities at the screen by adding probabilities for what are formally the ‘trajectories’ followed by individual electrons. The decoherent histories or consistent histories formalism (originating with Griffiths 1984; Omnès 1988, 1989; and Gell-Mann and Hartle 1990) takes this as the defining feature of decoherence. (See also the entry on the  consistent histories approach to quantum mechanics.  There are some differences between the various authors, but we shall gloss them  over.[6])