From so + be + it.
"Not by rough tongues and ready fists
Can you hope to jilt in the modern lists.
The armies of a littler folk
Shall pass you under the victor's yoke,
Sobeit a nation that trains her sons
To ride their horses and point their guns."
Alan Seeger; A Message to America; 1915.
So, when do we use one word and when do we use three? Is it interchangeable?