The division of words to syllables is largely conventional, but it relates to real phenomena in pronunciation. A syllable break does not break the flow of sounds, but it may affect the relative strengths of sounds. For example, the Finnish word maanosa is a compound that consists of the parts maan and osa. This division is also a syllable break, and this means that there is a secondary stress on the syllable o, giving the vowel higher strength. It is this stress, rather than any pause, that may create the impression of a two-part word.
Mostly syllable breaks do not cause any direct audible effect. Syllable division is, however, important for several reasons:
Syllable division is not the same thing as hyphenation as used for word division. Hyphenation is allowed at syllable breaks only, but not every syllable break is a permitted hyphenation point.
Syllables are important in Finnish due to their effect on consonant gradation, which is one form of stem variation. For example, the plural of lakki (cap) is lakit, where the double kk has turned into a single k.
In consonant gradation, the stem depends on whether a syllable is open or closed. In this context, the syllable concept is metric, and a syllable is open if it ends with a vowel (which can be a short vowel or a long vowel or part of a diphthong) and closed if it ends with a consonant. This can be alternatively formulated as follows: a syllable is closed if its vowels are followed by a consonant cluster or a word-final consonant.
To divide a word to syllables, we first need to split it to component words if it is a compound word (closed compound).
Otherwise, the syllable concept is defined so that there is a syllable boundary within a word before the last consonant of any consonant cluster. Thus, a single consonant between two vowels starts a syllable, and in when there are two consonants between two vowels, the syllable boundary is between the consonants.
There is also a syllable boundary between vowels, too, unless they form a long vowel or diphthong. In syllables other than the first one, diphthongs are possible only with i, u, or y as the second component (with few exceptions). It is not always possible to infer the location of syllable boundary in a group of three (or more) vowels without information about words and even their meanings. For example, the written form hauista can have the syllable structure hau.is.ta or the structure ha.uis.ta, depending on meaning. This spelling can be a form of three different words: hauis, hauki, haku. For the first two, the form hauista contains the diphthong au; for the third one, it contains the diphthong ui. In such words, it is permitted, but not common, to indicate the syllable boundary with a hyphen: hau’ista or ha’uista.
In the following examples, a period “.” is used to indicate syllable boundary:
As the examples show, there can be a syllable consisting of a single short vowel only at the start or at the end of a word. However, in word division, it is not permitted to separate such a syllable from the rest of a word, to another line. Thus, there are three syllables in the word keittiö, but only one permitted word division point (hyphenation point). The word asioin has three syllables, a.si.oin, but no good word division point.