Hello According to one of the tone adjustment ('tone sandhi') rules stated in various grammars/textbooks of Mandarin, two consecutive first tones T1+T1 are realized as T4+T1. Since Mandarin phrases may contain sequences of 2, 3, 4, 5…, perhaps even more, consecutive syllables with T1, and tone adjustment rules elsewhere apply across word boundaries, a primary tonal sequence like T1+T1+T1+T1+T1, as in “chu1 zu1 che1 si1 ji1” (= "taxi-driver"), may yield very different results depending on how the T1+T1>T4+T1 rule applies. For example, if the rule applied recursively irrespective of constituent structure, the outcome should be T4+T4+T4+T4+T1. If, on the contrary, the rule applied ‘cyclically’, bottom up, first to the smaller constituents [chu1 zu1] and [si1 ji1], then to the intermediate constituent [[chu1 zu1] che1], and finally to the whole noun phrase (or compound) [[[chu1 zu1] che1] [si1 ji1]], the result should probably be [[[T4+T1]+T1] [+T4+T1]]. There are still other possibilities, but such details are not clarified in the grammars/textbooks I have seen. When I made the Text-to-Speech Site Pal machine pronounce “chu1 zu1 che1 si1 ji1” for me, eight different native Mandarin voices respectively produced tonal sequences very approximately corresponding to the following ‘melodies’: 1. D + C sharp + C + B + B flat 2. C sharp + C + B + A + B flat 3. C + B + B flat + A flat + A 4. G sharp + G sharp + A + B flat + F sharp 5. A flat + A + B flat + B + F sharp 6. B + B flat + A + A + B flat 7. A + A + B + F sharp + F sharp 8. B flat + B flat + B flat + A + C Obviously, since I was not using special equipment, I cannot claim absolute accuracy, but I did listen carefully and searched for the pitch of each syllable on the piano keyboard several times and I can be reasonably sure that the tonal sequences and intervals used by those eight speakers correspond fairly closely to the melodies just transcribed. As you will observe, there are significant differences between 1, 2, 3 or 6, on one side, and 5, 7 or 8, for example (and Cantonese speakers at Text-to-Speech used still other pitch sequences I have not transcribed). My question, then, is this: How exactly does the T1+T1 > T4+T1 rule apply? And, in this particular case, is there a preferred tonal rendition of “chu1 zu1 che1 si1 ji1”, and how can the tonal-melodic differences above be explained? Thank you in advance.