Considering the increscent accord that grammar appears as language is employed in social interaction, how grammar occurs via interaction still stays greatly unknown. This inquiry shows that the onset of the apparition of constructions can be found in individual interactions. Through an examination on videotaped English conversations and corpora employing discourse analysis, conversation analysis, and corpus linguistic methodologies, it is found that conversational participants have a propensity as high as 80% or more to reuse words in previous turns. It is asserted that reuse as the resonance motivation mechanism and modification as the relevance motivation mechanism work competitively and commonly, forming the apparition of grammatical language structures. Reuses induce formation of the fixed frame; modifications constitute the category for an open slot. In summary, grammar appears via interaction amid participants who are continuously reusing and altering previous utterances to attain actual interactive aims.