Learn Hardcore German: Sowohl der Fahrplan als auch das Gleis ändern sich, wenn ein Gewitter kommt. - Both the timetable and the track change when a thunderstorm arrives.

sowohl … als auch is a correlative conjunction pair meaning both … and. You place the first element after sowohl and the second element after als auch to link two equally important parts of the sentence.

Why is there sich before ändern?

In German ändern can be used reflexively as sich ändern, meaning “to change” intransitively (“to change by itself”). The sich is the reflexive pronoun required by this verb form.

Why is the verb ändern plural (ändern sich) when Fahrplan and Gleis are singular nouns?

Because Fahrplan and Gleis are joined by sowohl … als auch, they form a plural compound subject. A compound subject requires a plural verb, hence ändern rather than ändert.

Why is there a comma before wenn, and why does the clause wenn ein Gewitter kommt appear at the end?

wenn introduces a subordinate (conditional) clause in German. Subordinate clauses are separated by commas and—in a main clause—generally placed at the end.

Why does kommt appear at the end of the wenn clause?

German subordinate clauses follow the verb-final rule: the conjugated verb moves to the end of the clause.

Why is the present tense used (ändern sich, kommt) when it refers to a future event?

German frequently uses the present tense for future events if context or time indicators (here wenn ein Gewitter kommt) make the timing clear. A future tense isn’t mandatory.

What case are der Fahrplan and das Gleis in, and why?

They are in the nominative case because they act as the subjects of the main clause. The subjects perform the action (they change).

Why is there no comma between Fahrplan and als auch das Gleis?

sowohl … als auch is a coordinating conjunction structure, which does not require a comma between the connected elements.