   However, according to Reid, a subset of natural signs lead us to think of what they signify without any prior experience. Members of this category “which, though we never before had any notion or conception of the things signified, do suggest it, or conjure it up, as it were, by a natural kind of magic, and at once give us a conception, and create a belief of it” (IHM 5.3, 60). Put your hand on a table, pause and experience the sensation of hardness. This tactile sensation leads us immediately to conceive of that which caused it as being hard, as having a certain resistive construction. But we are aware of the table's hardness, which caused the sensation, automatically. We do not understand why it is that we think of this special kind of physical constitution after having this kind of tactile sensation. Nonetheless, we must “conclude, that this connection is the effect of our constitution, and ought to be considered as an original principle of human nature” (IHM 5.3, 61). This is the defining feature of the kind of natural signs of which the tactile sensation of hardness is an instance: these signs lead us to conceive of what they signify simply because we are built in such a way as to have such conceptions on encountering such signs. Reid's approach to this relationship contrasts sharply with that taken by most advocates of the Way of Ideas, who attempted to posit a strong relationship between ideas of sensation and qualities of physical objects.