23.8 The discovery of laws of nature depends on the fact that in general certain simple types of character of active conditioning events repeat themselves. These are the normal causes of the recognitions of sense-objects. But there are abnormal causes and part of the task in the analysis of natural law is to understand how the abnormal causes are consistent with those laws. For example, the normal cause of the sight of a colour in a situation (near by) is the rectilinear transmission of light (during the specious present) from the situation to the percipient event through intervening events. The introduction of a mirror introduces abnormality. This is an abnormality of a minor sort. An example of major abnormality is when there is no transmission of light at all. The excessive consumption of alcohol produces delirium and illusions of sight. In this example the active conditioning events are of a totally different character from those involving the transmission of light. The perception is a delusion in the sense that it suggests the normal conditioning events instead of the abnormal conditioning events which have actually occurred. Abnormal conditioning events are in no way necessarily associated with error. For example, recollection and memory are perceptions with abnormal conditioning events; and indeed in any abnormal circumstances error only arises when the circumstances are not recognised for what they are. 23.9 Whereas the situations of a sense-object are always simultaneous with the associated percipient event, the active conditioning events are in general antecedent to it. These active conditioning events in general are divisible into two classes not very clearly separated, namely the generating events and the transmitting events. This classification is especially possible in the case of perception under normal circumstances. 24. Perceptual Objects. 24.1 Perceptual objects are the ordinary objects of common experience—chairs, tables, stones, trees. They have been termed 'permanent possibilities of sensation.' These objects are—at least for human beings—the most insistent of all natural objects. They are the 'things' which we see, touch, taste, and hear. The fact of the existence of such objects is among the greatest of all laws of nature, ranking with those from which space and time emerge. A perceptual object is recognised as an association of sense-objects in the same situation. The permanence of the association is the object which is recognised. It is not the case however that sense-objects are only perceived as associated in perceptual objects. There is always a perception of sense-objects—some sounds, for instance—not so associated. Furthermore, a sense-object associated in a perceptual object is perceived both as itself and as 'conveying' the perceptual object. For example, we see both the horse and the colour of the horse, but what we see (in the strict sense of the term) is simply colour in a situation.