A device used in writing phonological rules. The use of a Greek letter in a feature specification in place of a + or – indicates that the feature can take either a positive or negative value, but the same Greek letter must take the same value throughout the rule. This device is used to collapse a number of similar rules into one. For example, a language might display the following characteristics (1) the first of two adjacent obstruents must be voiced if the following obstruent is voiced (2) the first of two obstruents must be voiceless if the second is voiceless. One could write two rules to capture this:
(1) [-son] → [+voi] / ___ [-son, +voi]
(2) [-son] → [-voi] / ___ [-son, -voi]
This solution misses the generalisation that the first obstruent agrees with whatever voicing value the second obstruent has. Using a Greek letter variable the rules would be collapsed into:
[-son] → [αvoi] / ___ [-son, αvoi]
Sometimes it is necessary to capture the situation where segments disagree in the value for some feature. In this case a minus sign is used before the second occurrence of the Greek letter. Thus the rule:
[-son] → [αvoi] / ___ [-son, -αvoi]
says that if the second obstruent is voiced the first must be voiceless and if it is voiceless the first must be voiced.
Note that in feature specifications including more than one Greek letter variable, the different variables are independent. So, for example, [αson, βvoi] abbreviates the four specifications [+son, +voi], [+son, -voi], [-son, +voi] and [-son, -voi].
Also called alpha notation.