The suffix kin is often used for the same purposes as “also” and “too” are used in English. The word minäkin means “I, too” and could mostly be replaced by the words minä myös, but the suffix is a more normal expression in many contexts, especially when relating to the subject of a sentence.
For example, we can say Kävin Helsingissäkin or Kävin myös Helsingissä, “I visited Helsinki, too”, with hardly any difference in meaning. But to express “I, too, visited Helsinki”, the natural way is Minäkin kävin Helsingissä, though Myös minä kävin Helsingissä would be possible, too.
When used in such a meaning, kin is often more accurate than myös, since kin is attached to a specific word. Compare: Kävin kesällä Tukholmassakin (I visited Stockholm, too, in summer) vs. Kävin kesälläkin Tukholmassa (I visited Stockholm in summer, too).
When kin is attached to an attribute, it can mean “also”. For example, Hän myi uudenkin autonsa means “He sold his new car, too” (implying that he sold at least one other car too). However, in some contexts it has a completely different meaning. For example, the question Ostitko kalliinkin auton? does not normally mean “Did you buy an expensive car, too?” but rather asks whether the car bought is expensive or how much it cost. In such contexts, kin can be characterized as a tone particle (see the description of the hAn suffix) instead of meaning “also”.
When attached to a verb, kin sometimes means “also”, as in Kirjoitin ja soitinkin asiasta (I wrote about the matter, and phoned too). More often, it is a tone particle that expresses many different attitudes and feelings, like the hAn suffix, but it is not interchangeable with it. Examples:
The suffix kaan, kään is used in a sentence containing the negation verb, and it often corresponds to “either”, so that en minäkään tiedä means “I don’t know either”. We can say that the suffix kAAn is the negative-context counterpart of kin. This applies even when kin does not mean simply “also”. For example, just like Hän onkin jo tullut (Oh, he has come already) uses kin as a tone particle, the negative statement Hän ei olekaan vielä tullut (Oh, he has not come yet) uses kaan similarly.
The context need not be negative in form. In particular, kAAn is used in doubtful questions, possibly expecting a negative answer. For example, Kannattaako minun tulla? is a neutral question, “Is it worth my while to come?”, whereas Kannattaako minun tullakaan? expresses serious doubt about the matter; in English, we might add the word “really” to the question.
The suffix kAAn is often appended to the word silti (still, yet), with no particular effect on meaning or style, but siltikään is used especially when the sentence contains a negation.
There are many words and sayings that contain the kin suffix as an integral part, without the meaning described above. For example, the word kuitenkin means “however” or “yet”, and the suffix is really part of the word; kuiten does not exist as word. Yet, in a negative context, its kin is changed to kaan. For example, Kuitenkin huomenna sataa means “Yet it will rain tomorrow”, whereas the negative “Yet it will not rain tomorrow” is formulated as Kuitenkaan huomenna ei sada.
Similarly, kumpikin heistä (both of them) has the negative counterpart ei kumpikaan heistä (neither of them).
The negative pronouns mikään and kukaan ave the kAAn suffix appended directly to the old pronoun stems ku and mi.