辅音字符 th 有 清与浊 两种读音：
1 当位于词首时,可以从词性上判别其应有的读音.请看：
第一类：在以下 4种 词类 th 读 清音,即国际音标的 θ ：
a. Noun 名词：thing, theatre, thumb大拇指, thunder雷,
thermos热水瓶, Thursday, theory, theme, throat喉咙, thread线
b. Verb 动词：think, thank, throw, thrive, thicken,
c.Numeral 数词：three, thirteen, thirty, third, thousand
d.Adjective 形容词：thin, thick, thirsty, thoughtful,
thorough彻底的
第二类：在以下 两种 词类 th 读 浊音：
a. Pronoun 代词：they, them, their, theirs, this, these,
that, those, there, thy[旧时用法]你的
b. Functional terms 功能词：the, than, then, though, thus,
therefore
2 当位于词尾（或音节之尾）时,其读音多数是清音,如：bath, breath, both, cloth, tooth, health, wealth, arithmetic 等.只有在少数单词中,如：with, smooth 中读浊音.
3 当位于两个元音之间时,其读音多数是浊音.如：other, mother, brother, another, father, weather, feather, leather, further, breathe.
但是,也有读清音的.如在单词 method, nothing, anything, sympathy, sympathetic, mathematics, healthy, wealthy, Luther, Marathon(马拉松)等.