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Subjunction in logic means an if... then construction, as opposed to conjunction and and disjunction or.

In language a subjunction is a word that introduces a subordinate clause. It is also known, perhaps more commonly, as a subordinating conjunction. Examples include if, when, that, although, after, until.

I know that Oscar wears loud ties.
I will free you if you surrender your first-born to me.
These contrast with ordinary or coordinating conjunctions like and, or, but, then in that coordinate clauses are separable without violence to either, but subordinate ones depend for effect on their position embedded in their main clause. (Linguistically or is a conjunction too, unlike in formal logic.)

There would not be much point distinguishing the two classes unless they affected the grammar. In English some subjunctions may take the subjunctive mood: if I were...; that it be..., but this is not essential.

However, in German there is a distinction in word order as well. Some conjunctions are purely coordinating and make no difference to their constituents: such are und, oder, denn, aber. Others cause reversal of the verb and subject, and the true subjunctions move the subject to the end of the clause:

Er hatte sich sehr beeilt 'He had hurried a lot'
Er kam zu spät 'He came too late'
Er hatte sich sehr beeilt, aber ER KAM zu spät 'He had hurried a lot, but he came too late'
Er hatte sich sehr beeilt, trotzdem KAM ER zu spät 'He had hurried a lot, nevertheless he came too late'
Er kam zu spät, obwohl ER sich sehr beeilt HATTE 'He came too late, although he had hurried a lot'
www.lancs.ac.uk/staff/smithb1/companion/glossary.htm for the German grammar - I've altered the examples a bit so I hope I've still got them right. The pluperfect hatte 'had' sounds stilted in English but I don't want to go around questioning the sequence of tenses in German.