If in a language only one member of a customary phoneme opposition exists, the existing member of the opposition can take over (fully or partially) the articulatory peculiarities of the lacking member.
Standardized
IF only one member of a customary phoneme opposition exists, THEN the existing member of the opposition can take over (fully or partially) the articulatory peculiarities of the lacking member.
Finnish lacks the opposition s-ß , therefore s is spoken as , (Décsy 1970: 14-15).