Zu with Infinitives

Infinitives are usually preceded by zu except when modals are used.  If a separable prefix is used in the infinitive, the zu is inserted between the prefix and the stem.

Hast du Lust, den Dom zu besichtigen?  Do you feel like visiting the cathedral?
Es dauert lange, durch die Stadt zu fahren.  It takes a long time to drive through the city.
Es ist zu früh, sich aufzustehen.  It is too early to get up.

Um, ohne and anstatt can be used with zu as well.  They introduce infinitival clauses.  Um.. zu is used to indicate purpose, while ohne...zu and anstatt...zu are used with infinitives, and translated as present participles in English.  (Um...zu must be used instead of just zu when the English equivalent "in order to" can be used sensibly.)

Er kam, um das Buch abzuholen.  He came in order to pick up the book.
Sie sagte es, ohne mich anzusehen.  She said it, without looking at me.
Statt hier zu sitzen, sollten wir ihn suchen.  Instead of sitting here, we should look for him.

Sein + zu + an infinitive are used the same way in English and German, but the construction is far more common in German.

Das ist nicht zu machen.  That can't be done.
Das ist in jedem Laden zu finden.  That can be found in any store.

Expressions of Time

The accusative case is used to indicate definite time when no preposition is used.

Letzten Sonntag blieb ich zu Hause.  Last Sunday I stayed home.
Sie fährt nächste Woche nach Deutschland.  She's going to Germany next week.
Er hats uns voriges Jahr besucht.  He visited us last year.

Time expressions with the prepositions an, in and vor are in the dative case.

Wir müssen am Sonntag zurück.  We must return on Sunday.
In der Nacht wird es kalt.  It gets cold at night.
Vor drei Jahren war es hier genau so kalt.  Three years ago it was just as cold here.

The genitive case is used to express indefinite time, and may refer to the future or past.

Eines Tages war er krank.  One day he was sick.
Eines Morgens kommet er zu spät.  One morning he'll be late.

Subjunctive II (Conditional)

This subjunctive mood is used to make statements that are contrary to fact, instead of factual statements that are made in the indicative mood.  There are two forms of the German subjunctive: Subjunctive II and Subjunctive I.  Subjunctive II or the general subjunctive is used with if...then (wenn... dann) statements and conditional sentences.  Subjunctive I or special subjunctive is a less common mood that is used with indirect discourse.

The present tense of Subjunctive II is derived from the imperfect tense of the indicative.  For weak (regular) verbs, the subjunctive II is identical to the imperfect tense.  For strong (irregular) verbs, the present tense of the subjunctive II takes the past tense stem of the imperfect, adds an umlaut where possible, and adds the following endings:

Some exceptions include:

The past tense of Subjunctive II is derived from the past perfect tense of the indicative.  It is composed of a form of the subjunctive of sein or haben and a past participle.

Conditional sentences
These sentences are based on an if... then (wenn... dann) pattern in both English and German.  Dann can be omitted in these sentences also.  Remember that wenn is a subordinating conjunction, and forces the conjugated verb to the end of the clause.

Present Subj. II:  Wenn ich Zeit hätte, (dann) ginge ich ins Kino.  If I had time, (then) I would go to the movies.
Past Subj. II:  Wenn ich Zeit gehabt hätte, dann wäre ich ins Kino gegangen.  If I had had time, (then) I would have gone to the movies.

Wenn clauses may be introduced by a verb, and in this case, wenn disappears and dann may be replaced by so.

Kommt er heute nicht, (so) kommt er morgen.  If he's not coming today, then he'll come tomorrow.

A conditional sentence may begin with the dann clause as well; but dann is never used and the clause uses normal word order.

Wir trinken den Kaffee nicht, wenn er zu heiß ist.  We don't drink coffee if it is too hot.

Forms of würden + an infinitive
Würde and an infinitive translate to would + infinitive and is more common than the one word form in the dann clause.  Wenn clauses tend to avoid the würde construction, except with these eight verbs: helfen, stehen, sterben, werfen, brennen, kennen, nennen, and rennen.  These eight verbs use the würde construction in the wenn clause because the one word forms are archaic.  Moreover, conversational German tends to replace many subjunctive II forms of strong verbs with the würde construction.  However, this construction cannot be used with modal auxiliaries, haben or sein.