 Two terms are used for the mind’s shift from a non-intentional sensation to a perception. The sensation is a “sign” to the mind of the presence of the quality that causes it, in particular, a natural sign grounded in the constitution of our nature (Reid 1785 [2002: 119]). The sensation “suggests” a certain conception and firm belief; the one is “naturally and necessarily annexed” to the others. The transition is non-inferential, not due to habit, experience, or education. It follows, according to Reid, that the conjunction of acts is a consequence of the naturally inexplicable constitution of human nature (Reid 1764 [1997: 7–8, 40–44]; 1785 [2002: 96–101]).