A syllable ending in a simple vowel or diphthong is called open: one ending in a consonant or the aspiration is called closed. E.g. I-sä, father, tuo-da, to bring, consist of open syllables: kis-sat, cats, kir-jat, books, of closed.
As already stated, a word cannot begin or end with more than one consonant.
If a double consonant occurs in the middle of a word the first letter must be pronounced with the preceding vowel and the second with the succeeding, e.g. pal-lo, not pall-o.
1. (1) At the end of the first syllable of a word two consonants are tolerated, provided the first be l, r, n, or m, and the second k, t, p, or s. Pilk-ku, a spot, kent-tä, a field, simp-sukka, pearl: otherwise one of the consonants must be rejected.
2. (2) At the end of the second or succeeding syllables may stand only one consonant, and every word must end with a vowel or one of the consonants n, r, s, t, l (rare), or the aspiration.
If the grammatical changes cause an agglomeration of consonants which does not come under these rules, the consonants must be simplified or changed; syöks-tä becomes syöstä: avaim (for avaime) becomes avain.
One of the most characteristic features of the Finnish language is what is called the Harmony of the vowels. Besides the division of the vowels according to length, there is another by which they are classified according to their quality as follows:—
| Hard | a, o, u. |
| Soft | ä, ö, y. |
| Neutral | e, i. |
Long vowels and diphthongs belong to the same class as their component elements, which can never be discordant, that is to say, ay or äu are impossible combinations.