The multilingual (metropolitan Manila) Chinese Filipinos are currently engaged in a mixing practice that appears to incorporate features of Tagalog and English into the heritage language Hokkien (Southern Min). While most of the community refers to this practice as code-switching, it seems to behave more like a language, based on three criteria for languageness according to Haugen (1966) and Görlach (2002) – acquisition, acceptance, and attitude. This thesis investigates the remaining three criteria –codification, elaboration, and selection – and provides some evidence of languageness for the practice, which I refer to as Philippine Hybrid Hokkien (PHH). I do this by investigating one of its most distinctive features – derivational affixation mixing in the nominal domain. Adopting an experimental approach, I acquired the affixation mixing acceptability judgments of 63 Chinese (Filipino) respondents in the Philippines and subjected my data to statistical analyses using linear mixed-effects regression modeling. I found that Chinese Filipinos have high acceptability judgments for one or two-syllable Tagalog prefixes, which can to some extent be linked to the formation of community conventions. Testing to see if social factors affect the respondents’ judgments, I discovered that only age had a significant effect. I make four major observations from an apparent-time perspective. First, instead of the three distinct groups young (20s-30s), middle (40s-60s), and old (70s-80s) that my ethnographic notes had led me to propose, there are basically only two distinct groups of Chinese (Filipinos) in my dataset, that is, the 80s group vs. the 20s-70s group. The discovered two-way split also then prompted me to hypothesize that PHH did not emerge in the (pre)colonial era nor the 1920s, as I had suggested in my earlier research (Gonzales 2017), but most likely the 1950s. Second, my investigation highlights the nativization of PHH through education and Chinese Filipino identity-forming processes over the decades. This is manifested in the influence and acceptance of Tagalog affixes, in contrast to English, which has failed to permeate through PHH, except in cases where humor or creativity is involved. Finally, I found that while all Chinese Filipinos in the sample group believe that language mixing with Tagalog, English, and Hokkien in general is acceptable, only Chinese Filipinos younger than 80 are actively involved in the mixing practice, as evidenced in the affixation mixing data. This suggests that these younger speakers are taking ownership of their nativized mixed heritage variety. Taking all of the findings in this thesis and other databanks into consideration, I demonstrate that PHH fulfills all six of Haugen and Görlach’s main criteria. Comparing PHH with selected mixed languages with regard to certain social and structural factors, there is some evidence that it is a mixed language, but not a typical one.