A useful method is to ask five questions about each letter: hams or jahr? shiddah, rikhawah, or tawassut? istiʿla or istifal? itbaq or infitah? idhlaq or ismat?
ص: hams, rikhawah, istiʿla, itbaq, ismat.
ت: hams, shiddah, istifal, infitah, ismat.
ل: jahr, tawassut, istifal, infitah, idhlaq.
The opposition operates within a particular contrasting pair; qualities from different pairs can describe the same consonant. The non-opposing qualities add further identifying features to particular letters.