English preposition from and the secondary preposition out-of are essentially identical in terms of their functions of marking the point of departure, i.e. ablative. Despite the shared commonalities, however, the two prepositions exhibit a range of differences. Of intriguing relationship among polysemies of our-of is one of antonymy noted in Rhee (1996, 2000), where out-of can mark ``association`` as well as ``privation`` or ``dissociation``. Unlike out-of from does not exhibit such semantic versatility, and the usage closest to ``dissociation`` of from is designating an object that needs to be separated for the sake of protection or prevention. This research is an endeavor to look into the factors that enable and limit the range of functions of these near-synonymous prepositions. The limiting factors are largely due to the fact that our-of developed from a periphrasis with the compositional meaning from the motional/directional adverbial out and directional preposition of whereas the original adjectival/adverbial ``forward`` meaning of from engendered ``onward``. ``on the way``, ``away``, etc., and underwent categorial shift into a preposition. The fact that source constructions of grammatical markers not only affect the change but also determine the path and the result strongly supports the source determination hypothesis. A comparison of the two forms reveals interesting aspects with respect to principles and mechanisms in grammaticalization, including (1) semantic persistence, (2) functional specialization, (3) perspective shifts, (4) subjectification, (5) categorial and semantic divergence, among others. (Hankuk Uiiverity of Foreign Studies).