Whether "-d-" or "-t-" is used depends on the final consonant of the verb stem. If the stem ends in a voiceless consonant, then "-t-" is used, otherwise "-d-". It is often summarised with the mnemonic "'t kofschip": if the verb stem ends with one of the consonants of '"t kofschip" ("t, k, f, s, ch, p"), then the past tense will have "-t-". However, it also applies for "c", "q" and "x" and any other letter that is voiceless in pronunciation.