Context

In the opening section, the author had distinguished impressions and ideas as two kinds of impressions. The present section makes a further distinction of kinds of perceptions.

Background

According to Locke, all ideas have their origin in experience, which is of two kinds: “about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves.” He will call ideas originating from external sensible objects “sensations,” in contrast to ideas of reflection, such as “perception, thinking, doubting, believing, reasoning, knowing, willing, and all the different actings of our mind.” The having of ideas begins with sensation, which is required for any operations of the mind about which we can reflect. Because he is concerned only with the understanding, Locke does not investigate the physical basis of sensation or reflection. “I shall not at present meddle with the physical consideration of the mind; or trouble myself to examine . . . by what motions of our spirits or alterations of our bodies we come to have any sensation by our organs or ideas in our understandings; and whether these ideas do in their formation, any or all of them, depend on matter or not” (Essay, Introduction).

The Treatise

Method seems to require that we investigate impressions before we examine ideas, since (with very rare exceptions), it seems that impressions exist prior to the ideas corresponding to them. There are two kinds of impressions: impressions of sensation and impressions of reflection. “The first kind arise in the soul originally, from unknown causes.” [The author has at this point given the reader no reason to think that the causes of impressions are unknown.] Impressions of reflection are “deriv’d in a great measure from our ideas.” The manner in which these ideas arise is described, using examples. The first step is the production of an impression, which “strikes upon the senses.” The impression makes us perceive something, either heat or cold, thirst or hunger, pleasure or pain, etc. The mind then “takes” a copy of the impression, and the copy remains after the impression has ceased to be. This copy is called an idea. In the case of pleasure or pain, the idea, “when it returns upon the soul,” gives rise to impressions of reflection, such as desire and aversion, hope and fear, and so on. The reason they are properly called “impressions of reflection” is that they are derived from reflection. [The author seems to mean that they arise when we “reflect” upon (which here seems to mean “think about”) the ideas of pleasure and pain which precede the impression.] The resulting impressions are themselves “copy’d by the memory and imagination,” whence they become ideas. These ideas (of desire and aversion, etc.) may themselves give rise to further impressions, which may give rise to further ideas. Thus the process is recursive, in the sense that it can use its previous outputs as new inputs into the process. The result is that impressions of reflection occur before the ideas of reflection, but after the ideas of sensation, from which they are derived. The task of understanding our sensations “belongs more to the anatomists and natural philosophers than to moral.” For this reason, it will not be undertaken in the present treatise on moral philosophy [which is concerned solely with the human understanding]. Because the impressions of reflection (passions, desires, and emotions), which are the subject of the treatise, are derived from ideas, it will be “necessary” to reverse the method which seems most natural, i.e., to examine impressions first, “and in order to explain the nature and principles of the human mind, give a particular account of ideas, before we proceed to impressions.” The author states that it is this reason that has led him to choose “to begin with ideas.”

The Enquiry

In the Enquiry concerning Human Understanding, Section 2, “Of the Origin of Ideas,” Hume does not make an explicit distinction between perceptions of sensation and of reflection. However, he does use similar language: “all the materials of thinking are derived either from our outward or inward sentiment” or “feeling.” Outward sentiment is sensation, such as the pain of excessive heat, and inward sentiment is described variously as “passion” and “affections.”