  Reid provides additional criticisms of Hume’s account of memory. First, Reid interprets Hume’s account of memory as committing him to the position that we have the power to repeat ideas (though notice that Hume does not commit to this in the quoted passage). Reid argues that this position is inconsistent with Hume’s claim that impressions are the efficient causes of ideas. Reid’s second criticism is more insightful; he argues that differences in degrees of force and vivacity are insufficient to sustain the distinctions between perception, memory and imagination. Reid interprets Hume as holding that these three faculties do not differ in kind, but rather in the degree of force and vivacity of the ideas that are their objects. Ideas with the greatest degree of force and vivacity are perceptions, those with a lesser degree are memories, and those with the least degree of force and vivacity are imaginings. Reid criticizes this taxonomy on phenomenological grounds. Some perceptions are less forceful and lively than some memories, as when lost in reminiscence, and some memories are less forceful and lively than imaginings, as when lost in reverie. Furthermore, increasing the degree of force and vivacity does not transform a memory or an imagining into a perception. Reid compares striking one’s head against the wall to lightly touching it to the wall. The latter has much less force and vivacity than the former, yet lightly touching one’s head to the wall is neither a memory nor an imagining (Essays, 289).