都可以引导让步状语从句，但不能和but连用

但是though可以做副词，意为“可是，然而”，置于句末。如：
he said he would come;he didn't,though.

though引导的从句可以像as引导的从句一样用倒装语序，但是although引导的从句只能用正常语序。例如：
smart though/as he is, she studies hard
though she is smart, she studies hard.
although she is smart, she studies hard.
但是不能说：smart although she is, she studies hard
as she is smart, she studies hard.都是错误的。