Atkinson's definition of conception is redundant to the process he mentioned under "concepts" in the previous chapter: it is gathering together a group of similar objects from direct or secondary information, recognizing their similarity as a class, and then abstracting the characteristics that define the class.
It is the quality of abstraction that lends sophistication to thought: animals are utterly incapable of making abstractions, and children do not develop the skill in the earliest years of life: they recognize things such as they are, and ascribe to each thing an individual identity, but do not discern basic properties. An infant or toddler recognizes the members of its family from memory and identity - father, mother, sister, brother, but does not recognize the difference between child and adult, male and female - everything is in its own class.
(EN: In the case of children, this is exaggerated to the point of being misleading. There is a brief period when a child may point at a thing and call it by the wrong name, such as pointing at a dog and saying "cat," but it is not long before they sort it out and begin to identify things properly - to see an animal they never before encountered and properly pronounce it to be a dog. This demonstrates the ability to understand the concept of dog, as it is not merely identification of a specific known item whose name has been taught.)
Abstraction is largely the result of attention - specifically, attention to the details about a specific thing. In order to recognize similarities and differences, one must first be attentive to the qualities and characteristics of things - and people who are not attentive cannot be discerning.
For example, most people recognize basic types of cars - they can tell a sedan from a coupe from a roadster - but someone who is enthusiastic about automobiles can tell the exact year, make, and model of a vehicle they have seen at a glance. This is because they have been attentive and recognition of the qualities and their association to class become virtually instantaneous.
Comparison and Classification
Conception departs from mere perception and memory when things are compared to one another and likenesses and differences are appreciated. We generally recognize when two things are similar or different, though things are seldom identical or wholly dissimilar - and as such we begin to evaluate the ways in which they are alike and different. When two things are found to be more alike than different, we consider them to be members of the same general class, and then begin to consider the qualities that make them so as opposed to the qualities whose presence is incidental.
Form there, we arrive at the notion of classification, by which we believe that objects that meet certain criteria fall into the same class, and become aware of the properties that are general to all members of the class. Our classifications tend to be hierarchical - we first recognize the differences between living and non-living objects, then divide the living into plants and animals, then divide the animals into an array of sub-classes, each of which is subdivided further.
The method of biological classification serves as a clear example of the method of classification in general: the domain, kingdom, phylum, class, order, family, genus, and species of a specific creature shows a narrowing system of categories that classify every species on the planet.
Likewise, the method of categorizing books aptly demonstrates the manner in which all human knowledge is divided into major classes, then subdivided repeatedly to arrive at a specific topic.