We use the set expression 按说 to make an assumption or express a point of view which is based on our own experience or common sense.
We should state it before a subject or a predicate.
He's supposed to be at home
tā ànshuō yīnggāi zài jiā
We're supposed to win
ànshuō wǒmen yīnggāi yíng
A child of this age should know how to behave
zhème dà de háizi, ànshuō gāi dǒng shì le
We usually use the set expression 按说 with an adversative conjunction meaning “but”.
Examples include 可 , 可是 , 但是 , or 不过 . Each of these adversative conjunctions introduce the opposite idea of what was stated.
It is supposed to be spring, but the weather is still very cold