The dash and hyphen are often confused but serve different purposes. The dash is longer and used to interrupt or add an aside to a sentence. The hyphen is shorter and used to join words or word parts, such as in "mother-in-law" or "two-thirds". Hyphens are also used when combining words before a noun, such as "strong-willed father" or with prefixes like "self-", "quasi-", "ex-", and in fractions.