Provided that and unless
Sofern sets a condition meaning provided that and introduces a verb-final clause. Es sei denn means unless; when followed directly by a main clause, that clause keeps verb-second order.
Understand the idea
Restrictive conditions define when a statement holds or identify an exception that cancels it. Sofern often means provided that, while es sei denn introduces an unless-type exception. Their meanings and following word order differ.
Build it step by step
A sofern-clause is subordinate and has a final finite verb. Directly after es sei denn, an ordinary main-clause pattern can follow. An added dass changes that continuation into a subordinate clause. Keep the condition or exception attached to a clear main statement so the reader knows what is restricted.
See it in a sentence
Wir kommen, sofern wir Zeit haben.
Du kannst teilnehmen, sofern du dich anmeldest.
A useful memory aid
State the main rule first, then add either its requirement or its exception. This makes the distinction between provided that and unless concrete.
A common trap
Do not combine es sei denn with verb-final order automatically. Check whether the following structure is a direct main clause or an added dass-clause.