The first syllable of a word takes the main stress. The stress is primarily a matter of strength of voice, rather than tonal (musical). The simple stress principle greatly helps in recognizing word boundaries from Finnish speech: a stressed syllable starts a new word. Very short words that are grammatical rather than content words (such as on “is”) are often unstressed, however.
The simple stress principle is so strong that it also applies to new loanwords and usually even to foreign names. In educated speech, foreign words from some languages, like French, may sometimes take the stress of the original language. More often, there is “simulated stress”. For example, a French word like gourmet is pronounced as gurmee (or kurmee), with stress on the first syllable, but the vowel of the second syllable (which is stressed in French, when the word is spoken as isolated) is clearly long. The vowel length thus somewhat imitates the French stress.
There are a few exceptions to the main stress principle. In some styles of pronunciation in colloquial language, a word like kiitos (thank you) often has stress on the second syllable. It might even be pronounced so that the first syllable is barely audible or not pronounced at all: tos. A word like aivan (right so, exactly) might be pronounced with main stress on both syllables (áiván) or with main stress on the second syllable (aiván). In emphatic pronunciation, the word todellakin (indeed) may get stressed as todellákin.
In a compound word (closed compound), the first syllable of the second part usually has secondary stress in Finnish. Thus, if we denote primary stress with the acute accent (´) and secondary stress with the grave accent (`), the compound aikataulu, from aika (time) and taulu (table), is pronounced áikatàulu.
No stress marks are ever used in normal Finnish writing. Sometimes a written word is ambiguous in the sense that it can be a compound or a non-compound word, and the context is needed to resolve the ambiguity. For example, piilevä (hidden) is normally a participle of piillä (to be hidden), but in some contexts, it can be a compound word consisting of pii (silicon) and levä (alga), thus pronounced píilèvä, meaning a small organism, diatom. It is in principle permitted, but not common, to use a hyphen in such words for clarity: pii-levä.
Secondary stress may appear in a non-compound word, too, if it consists of four syllables or more. The rules are complicated, but the basic rule is that secondary stress appears on the 3rd, 5th, 7th, etc. syllable, but never on the last syllable. If a word is longer than four syllables and the 3rd syllable is short (ends with a short vowel), secondary stress usually moves forward and thus appears on the 4th, 6th, 8th, etc. syllable.
The following examples illustrate the basic rules:
The main complication to the basic rules is that some relatively long derivational suffixes such as lAinen, mAinen and minen have secondary stress on their first syllable. In this sense, they are treated as parts of a compound word. For example, we have áuttamìsella (with helping; inflected form of auttaminen), even though mi is short, and rómahdusmàinen (crash-like, catastrophical), even though dus is long.
The secondary stresses create a rhythm into long compound words. For example, kaupallistuminen (commercialization) is pronounced as káupallìstumìnen and keskusteluissammekin (in our discussions, too) is pronounced as késkustelùissammèkin (since the third syllable te is short).