Colloquial Finnish refers to spoken varieties of Finnish. Their use is widespread in all situations that are not strictly formal. While the traditional dialects have been eroded somewhat, colloquial Finnish can still vary significantly by region. In addition, the diglossia exhibited by Finnish between the written standard and the spoken vernacular exhibits a gradient, with the most informal varieties e.g. using slang, while somewhat more formal varieties would not, and would in general be closer to standard Finnish.
This page describes perhaps the most common variety of colloquial Finnish, spoken in the capital region (in or near the capital Helsinki), but also more widely particularly cities in Tavastia (the Tavastian dialects represent perhaps the single most influential dialect group on the variety spoken in Helsinki, which is still however a blend of basically all dialects to at least some degree). Its influence is significant on the other varieties as well. Features of the so called Helsinki slang are not discussed on this page, however.
Traditionally, colloquial Finnish was rarely written, but this is now common in informal conversations (e.g. on online chatrooms).
The native Finnish /d/ and /ts/ vary greatly in dialects. In colloquial Finnish, the result often depends on the word, as more obscure (or 'bookish' or technical) words tend to be pronounced like in standard Finnish. However, in more common words, the following rules often apply.
Native /d/ usually surfaces as /d/ like in standard Finnish, except in /hd/, where it is usually lost. In some cases, it may be lost in general as in the eastern dialects, remaining as /h/ after a long vowel (or in some cases lost entirely and replaced with a hiatus), /j/ after /i/ and /ʋ/ after /u/ or /y/.
Native /ts/ may be either /ts/ (without gradation) or : (⟨tt⟩ : ⟨t⟩).
Word-final -n is usually lost in the illative ending and passive/impersonal verb endings (except in the imperative mood, but the passive/impersonal imperative is rarely used in colloquial Finnish anyway). Sometimes the genitive ending is replaced with final gemination, but if this results in ambiguity (such as a form that is otherwise equivalent to the nominative singular), this may often be avoided. There are also many forms where -n is never dropped, such as first-person singular verb endings.
The result is that many partitive and illative forms fall together. The final -n may not be dropped if this causes (overt) ambiguity.
Some other word-final consonants are dropped (or rather replaced by final gemination) more sporadically. The most common regular rule is the replacement of final -t with final gemination or dropping as part of the participle/perfect ending -nut:
Word-final vowels are dropped a lot more often. If a word-final vowel is dropped and the final consonant is geminated (long), it becomes ungeminated (short), as usual. Consonant clusters are not simplified, however.
The final -a/-ä in the inessive (-ssa), elative (-sta), adessive (-lla) and ablative (-lta) endings is often dropped.
This also extends to particular words.
Word-final -si is often simplified to just -s in polysyllabic words. This affects many different forms.
Clitics count as the "end" of the word when dropping final vowels, but not when dropping final consonants; indeed, they may be subject to the latter.
Unstressed -Vi- diphthongs (in open syllables) often simplify to just -V- when this does not result in ambiguity.
Unstressed vowel sequences with a hiatus are often simplified in specific contexts. This particularly affects the partitive ending (which often assimilates to the preceding vowel) and the adjective suffix -ea (which becomes -ee, the partitive of which then often has a -t-), but does also affect e.g. certain verbs. The former will cause many partitive and illative singular forms to fall together (in addition to those cases caused by the final -n being dropped), but this is usually not an issue; if it is, the final -n of the illative is kept (simplification takes priority).
The opening diphthongs ⟨ie⟩ /ie̯/, ⟨uo⟩ /uo̯/, ⟨yö⟩ /yø̯/ usually simplify to just ⟨ii⟩ /iː/, ⟨uu⟩ /uː/, ⟨yy⟩ /yː/ when immediately followed by a vowel, such as due to a lost consonant.
The interrogative clitic -ko is often -ks. If preceded by certain consonants (e.g. -t-), the result often depends on the speaker.
While Standard Finnish is pro-drop, in that first-person and second-person pronouns are rarely used if they are otherwise clear from e.g. a verb form or possessive suffix, colloquial Finnish does generally not drop pronouns. Possessive suffixes are not really used in colloquial Finnish outside of certain expressions to begin with, and the genitive form of the pronoun is instead used to express possession (although the second-person singular possessive suffix in particular may sometimes still be used, often in the form -s as per usual dropping of final vowels).
The passive/impersonal form is often used in place of the first-person plural forms of verbs. This applies to all tenses and moods. The first-person plural pronoun may actually be dropped in this case contrary to the previous rule.
The third-person plural forms are in turn often replaced by third-person singular forms.
The so-called kaksoispassiivi (“double passive”) is ubiquitous in colloquial Finnish.
Due to foreign (especially Swedish) influence, yks(i) (literally “one”) and se (literally “that”) may be encountered as indefinite ("a", "an") and definite ("the") articles, respectively.
The following grammatical forms are rarely used:
Short forms of common verbs (characteristic of the Tavastian dialects) are common in colloquial Finnish. This includes the verbs olla, tulla, mennä and panna (-VCe- becomes -V:-). In addition, the present stem näe- of nähdä is often reduced to nää-. Infinitive and participle forms are not affected.
The short forms of third infinitive illative forms are also seen quite often: