Adverbs
The most productive way to form adverbs is to derive them from the neuter singular form of the corresponding adjective (бързо (fast), силно (hard), странно (strange), although adjectives ending in -ки use the masculine singular form, also in -ки, instead: юнашки (heroically), мъжки (bravely, like a man), майсторски (skilfully). The same pattern is used to form adverbs from the (adjective-like) ordinal numerals, e.g. първо (firstly), второ (secondly), трето (thirdly), and in some cases from (adjective-like) cardinal numerals, e.g. двойно (twice as/double), тройно (three times as), петорно (five times as).
The remaining adverbs are formed in ways that are no longer productive in the language. A small number are original (not derived from other words), for example: тук (here), там (there), вътре (inside), вън (outside), много (very/much) etc. The rest are mostly fossilized case forms, such as:
- archaic locative forms of some adjectives, e.g. добре (well), зле (badly), твърде (too, rather), and nouns горе (up), утре (tomorrow), лете (in the summer);
- archaic instrumental forms of some adjectives, e.g. тихом (quietly), скришом (furtively), слепешком (blindly), and nouns, e.g. денем (during the day), нощем (during the night), редом (one next to the other), духом (spiritually), цифром (in figures), словом (with words); or verbs: тичешком (while running), лежешком (while lying), стоешком (while standing).
- archaic accusative forms of some nouns: днес (today), нощес (tonight), сутрин (in the morning), зиме/зимъс (in winter);
- archaic genitive forms of some nouns: довечера (tonight), снощи (last night), вчера (yesterday);
- homonymous and etymologically identical to the feminine singular form of the corresponding adjective used with the definite article: здравата (hard), слепешката (gropingly); the same pattern has been applied to some verbs, e.g. тичешката (while running), лежешката (while lying), стоешката (while standing).
- derived from cardinal numerals by means of a non-productive suffix: веднъж (once), дваж (twice), триж (thrice);
Adverbs can sometimes be reduplicated to emphasize the qualitative or quantitative properties of actions, moods or relations as performed by the subject of the sentence: "бавно-бавно" ("rather slowly"), "едва-едва" ("with great difficulty"), "съвсем-съвсем" ("quite", "thoroughly").