思

Bottom heart - the indexing radical. In classical Chinese psychology the heart is the seat of both feeling and thinking, so 思 belongs naturally to the family of mental verbs alongside 想 (think), 念 (remember), 感 (feel), 忘 (forget). The brain-above-heart picture gave the original sense to ponder: head and heart working together.

Top is graphically 田 but historically a contraction of 囟 (fontanelle, the soft spot on a babys skull) - the seat of thinking in classical physiology. The original picture was brain-and-skull above heart, the two organs producing thought together. The modern script regularized the shape into the field square 田.