classic waka stream

If from the valley
no voice of the bush warbler
were to come forth,
who then would ever know
that spring has come at all?

Meaning
If the bush warbler did not come forth from the valley with its cry, who would ever know that spring has come?
Commentary
Spring Songs, Book One

By imagining the opposite of reality—if there were no cry of the bush warbler—the poet brings out the conjecture in the latter lines.
This is an example of a counterfactual expression.
Author
Oe no Chisato
Source
Kokin Wakashu
Other