Boucher and Osgood (1969) referred to the difference between [E+] (E plus) elements and [E –] (E minus) elements in vocabulary, and showed that positive [E+] elements are more productive, are used more frequently, and appear earlier in the process of language acquisition. Following Jespersen (1917), Zimmer (1964) discussed the morphological irreversibility of negative affixation, such as ‘well-unwell,’ and ‘sick’, but never *‘unsick’. In fact, he found it is hard to conceptualize negatively formed negations such as *‘unvanish’ or *‘nonabsence’.1