Several early texts (below) use an interchangeable synonym of ying < Old Chinese *[q](r)əәŋ 應 "respond; resonate" : dòng < *[Cəә-m-]tˤoŋʔ 動 "move; shake; set in motion".
Both the logographs gǎn 感 and yìng 應 are classified as radical-phonetic characters written with the "heart-mind radical" 心 (typically used to write words for feelings and thoughts) and phonetic indicators of xián 咸 "all; Hexagram 31" and yīng 鷹 "hawk; eagle" minus the "bird radical" 鳥 (Bishop 2012).