[2] Originally, the terms were used to refer to an impressionistic sense of strength differences, though more sophisticated instruments eventually gave the opportunity to search for the acoustic and articulatory signs.
For example, Malécot (1968) tested whether articulatory strength could be detected by measuring the force of the contact between the articulators or of the peak pressure in the mouth.
Because such studies initially found little to substantiate the terminology, phoneticians have largely ceased using them, though they are still commonly used as "phonological labels for specifying a dichotomy when used language-specifically.
The articulators in the mouth can move with a greater velocity[4] and/or with higher electromyographic activation levels of the relevant articulatory muscles[5] with fortis consonants than with lenis ones.
[11] "Fortis" and "lenis" have also been used to refer to contrasts of consonant duration in languages like Jawoyn,[12] Ojibwe,[13] Dalabon, Kunwinjku,[14] and Zurich German.
The intensity of the pronunciation leads to a natural lengthening of the duration of the sound, and that is why strong [consonants] differ from weak ones by greater length.
In English, use of the terms "fortis" and "lenis" is useful to refer to contrasts between consonants that have different phonetic attributes depending on context.
For instance, for the transcription of the Zürich German fortis–lenis contrast – which involves neither voicing nor aspiration –, notations such as the following ones have appeared in the relevant literature:[20] This means that depending on the system, ⟨p t k f s ʃ x⟩ may have opposite values, i.e. they may represent either fortis or lenis sounds.