Compound words are commonly used in Finnish. Sometimes it’s very hard to determine if the words should be written separately or together. Even natives make a lot of mistakes. In this case hyphen is used between the compound words, because the words are equally valued: englantilainen does not determine suomalainen. Another example is Matemaattis-luonnontieteellinen tiedekunta (”Faculty of mathematics and science”). These cases occur rarely. The -nen of englantilainen changes to –s because it’s the first part of the compound word. This happens even without hyphen (suomalaispoika = a Finnish boy). Another cases when you use hyphen between compound words are if one of the words is a proper noun (pohjois-Eurooppa = Northern Europe, Mikko-setä = uncle Mikko) or for clarity when the first word ends with the same wovel than the second begins (ruoka-aika = mealtime).