In German, the past participle is formed one of three ways:

1. For regular or "weak" verbs, add the prefix ge- and the suffix -t, e.g. lieben -> geliebt.

2. For strong verbs, add the prefix ge- and the suffix -en, with whatever sound change (ablaut) occurs in the root, e.g. singen -> gesungen.

3. For irregular verbs, the past participle will still have the ge- prefix, but the formation of the rest of the word might be a weak/strong mix, e.g. bringen -> gebracht, or it may come from a different root entirely, e.g. sein -> gewesen, or it may altered due to euphony, e.g. essen -> gegessen.

The ge- prefix is not added if the first syllable is unstressed, e.g. verschlafen -> verschlafen, gestehen -> gestanden (word already has ge- prefix), entziehen -> entzogen, addieren -> addiert.

For verbs with stressed prefixes (which are normally separable prefixes or compound verbs) the -ge- is inserted between the prefix and the root, e.g. angreifen -> angegriffen, zutun -> zugetan, old spelling stehenbleiben -> stehengeblieben (now stehen geblieben)--but not if the -ge- would be added in front of an unstressed syllable, e.g. zubereiten -> zubereitet.

Certain modal verbs and causative "lassen" use an infinitive in place of a past participle in compound tense formations with a main verb, e.g. "ich habe es telc b1 kaufen sollen," but if the main verb is missing then the participle is normal, e.g. "ich habe es gesollt."