Let us see, however, how things look when we try to =describe= attention, without making any effort to interpret or explain it. Suppose that, as I sit writing this paragraph, I am called to the telephone, or am interrupted by the entrance of a friend. My attention is thus diverted to a new object. What happens? Something happens that we can only describe as =a shift of the vividness of our mental processes=. A moment ago, my psychological ideas were vivid, set (as it were) in the focus of attention, while all other ideas and perceptions were dim and marginal; now the incoming ideas—my friend’s business or the subject of the message—drive to the front; they in their turn become vivid and focal, while the psychological ideas, just lately central and dominant, fall back, along with the perception of my sensory surroundings, into the dim background. _Attention, therefore, if we consider it purely descriptively, hinges not upon mental activity, but upon the vividness of mental processes_; and the state of attention may be described as a certain pattern or arrangement of mental processes; whenever our experience shows the pattern of vivid centre and dim background, of bright focus and obscure margin, then we have attention before us. What, then, is =vividness=? The answer has been given already (p. 66): vividness is _one of the universal aspects or attributes of sensation_. Just as all sensations vary in intensity, so do all sensations vary in vividness. If you want a more positive answer; if you want to know how precisely vividness ‘feels’ in experience; observe your mental processes now, as you are puzzling over this book; the difference between foreground and background, focus and margin,—between the dominant ideas aroused by what you read, and the obscure perceptions derived from your surroundings,—will show itself at any rate in the rough. _Be careful not to confuse vividness with intensity_: when you are listening intently for a very faint sound, the sound, as it comes, is the most vivid experience you have, although it is near the lower limit of intensity; and when you are absorbed in your work, the sound of the dinner-gong in the hall may be very dim and obscure, although it is loud enough to be heard all over the house. _Be careful, too, not to confuse sensory vividness with definiteness of meaning_ (p. 29). A patch of colour in an oil-painting may strongly attract your attention, may thus be extremely vivid, and may yet be altogether unintelligible; and another patch of colour, that you have passed over with ‘half a glance’ and that remains permanently in the background of experience, may carry the perfectly definite meaning of a dead soldier. Differences of vividness are neither differences of strong and weak in sensation, nor of distinct and indistinct in understanding; they are more like differences of robust and weakly, or of self-assertive and retiring.