What are the tonal modifications to yī(一) and bù (不)?

yī:

When yī is read individually or is at the end of a word or a sentence, it should be pronounced in the original tone, the first tone.
When it is before the fourth tone, it should be modified to the second tone.
Examples:
一道yídào 一次yícì 一定yídìng 一致yízhì 一律yílǜ
一晃yíhuàng 一动yídòng 一并yíbìng 一刻yíkè 一路yílù

When it is before the first, the second and the third tone, it shall be modified to the fourth tone.
Examples:
before the first tone:
一般yìbān 一端yìduān 一经yìjīng 一边yìbiān
before the second tone:
一时yìshí 一群yìqún 一条yìtiáo 一团yìtuán
before the third tone:
一举yìjǚ 一早yìzǎo 一手yìshǒu 一体yìtǐ

When it is between two same verbs, it shall be modified to the light tone.
Examples:
看一看kànyikàn 想一想xiǎngyixiǎng
问一问wènyiwèn 学一学xuéyixué

bù:

When bù is read individually or is at the end of a sentence, it should be pronounced in the original tone, i.e. the fourth tone.
When it is before the fourth tone, it should be modified to the second tone.
Examples:
不会búhuì 不但búdàn 不论búlùn 不必búbì 不变búbiàn
不是búshì 不信búxìn 不料búliào 不愧búkuì 不错búcuò

When it is between two adjectives, between two verbs or between a verb and a complement, it should be modified to the light tone.
Examples:
好不好hǎobuhǎo 行不行xíngbuxíng
看不清kànbuqīng 打不开dǎbukāi

TAG: Fourth tonal tone What Examples fourth