Three forms, one Umlaut rule, two ways to say 'than'.

Add -er to the positive form of the adjective: klein → kleiner, schnell → schneller, neu → neuer. Adjectives ending in -el drop the e before adding -er (dunkel → dunkler). When used attributively (before a noun), the comparative takes full adjective endings: ein kleineres Kind, der schnellere Zug. When used predicatively (after sein, werden, bleiben), no additional ending is added: Das Kind ist kleiner.

German has two superlative forms with distinct uses. The predicative superlative is am + adjective + -sten (no adjective ending): Das Kind ist am kleinsten. The attributive superlative uses the definite article plus the adjective + -ste plus weak-declension endings: das kleinste Kind, die schönste Frau, den längsten Weg. A linking -e- is added when the stem ends in t, d, s, ß, x, or z: am ältesten, am heißesten. Both forms translate to English "the smallest" or "the most beautiful" — the split is German-specific.

Both mean "the most beautiful" in English but function differently in German. Am schönsten is predicative: it follows a linking verb (sein, werden, bleiben) and takes no adjective ending — Das Wetter ist am schönsten im Sommer. Die/der/das schönste is attributive: it precedes a noun and takes weak-declension endings — der schönste Tag, die schönste Frau, das schönste Lied. Never use am -sten before a noun, and never use the bare -ste form after a linking verb.

Almost all one-syllable adjectives whose stem vowel is a, o, or u take an umlaut in the comparative and superlative — this rule covers about 95% of cases: alt → älter, jung → jünger, kalt → kälter, warm → wärmer, groß → größer, lang → länger, kurz → kürzer, stark → stärker. Notable exceptions that do NOT umlaut include flach, klar, schlank, froh, and stolz. Multi-syllable adjectives almost never umlaut (schön → schöner, not umlaut).

Als is used after a comparative form to express inequality — Er ist größer als sie ("He is taller than she"). Wie is used in equal comparisons after so … wie — Er ist so groß wie sie ("He is as tall as she"). Using wie instead of als after a comparative is the single most common comparison error among English speakers, because English "than" maps to German als while English "as … as" maps to German so … wie. Never say *Er ist größer wie sie — this is grammatically wrong.

Four adjectives are fully suppletive — their comparative stem is unrelated to the positive form: gut → besser → am besten (good/better/best); viel → mehr → am meisten (much/more/most); hoch → höher → am höchsten (note: hoch drops the c in all inflected forms — höher, not hocher); nah → näher → am nächsten. The adverb gern also has an irregular series: gern → lieber → am liebsten. These five, together with the one-syllable umlaut group, account for virtually all the "irregular" comparatives learners encounter at A2–B1.

Use the je … desto or je … umso construction: Je mehr ich lerne, desto besser werde ich ("The more I learn, the better I get"). Je introduces a subordinate clause with verb-final word order; desto or umso opens the main clause with the comparative adjective in position 1 followed by V2 inversion. Both desto and umso are interchangeable in this construction — umso is slightly more informal. This construction is a B1 exam staple used extensively in formal writing and speaking tasks.

Yes, always. Comparative adjectives before a noun take the same strong, mixed, or weak endings as positive adjectives: ein größerer Mann (strong, masc. nom.), der größere Mann (weak, masc. nom.), einen größeren Mann (mixed, masc. acc.). Superlative adjectives before a noun always take weak endings because they always follow the definite article or a demonstrative: der/die/das + adjective + -ste + weak ending. The full weak-declension pattern for superlatives follows the same rules as adjective endings generally — see the adjective endings guide for the complete declension tables.