Units of Thought – In many ways, thought is simply an extension of perception and memory. When we perceive, we form a mental representation. When we remember, we try ton bring that mental representation to mind. When we think, we use representations to try to solve a problem or answer a question; often when we think we are actually just evaluating and organising our new and existing mental representations. Thinking means manipulating mental representations for any purpose.
Thinking in Words and Images – Most of the time, humans think with either word or images, or a combination of the two. The images that we conjure up in our mind are called mental images, such as images of our ideal holiday destination, or what we usually eat for breakfast.
People also frequently think using mental models, representations that describe, explain or predict the way things work. Mental models can be quite simple, like most people’s understanding of cars (if it doesn’t start, something must be wrong under the hood) or a child’s understanding of a cavity (a hurt tooth that means I have to go the dentist). On the other hand, mental models can be quite complex, such as the mental models used by the mechanic to troubleshoot a car, or a dentist’s understanding of how cavities are formed. While mental models often include visual elements, they also always include descriptions of the relationships among certain elements.
Concepts and Categories – Before people can think about an object, they usually have to classify it so that they know what it is and what it does. An approaching person is either a friend, stranger or enemy, a guitar is either acoustic or electric, a piece of food on the table is either a fruit or a vegetable, if it’s a fruit, that fruit is either an apple or an orange and so on. People will not think about an object until they have placed it in a mental drop down list of possible categories.
A concept is a mental representation of a category; that is, an internal portrait of a class of objects, ideas or events that share common properties. Some concepts can be visualised, but a concept is broader than it’s visual image. For example, the concept car stands for a class of transport vehicles with four wheels, seating space for at least one driver and one passenger and a generally predictable shape (schema). Other concepts, like honesty, defy visual representation, although they may have visual associations, such as an image of an honest face, or a person you view as being quite honest.
The process of identifying an object as being a part of a category is called categorisation. Categorisation is essential to thinking, because it allows people to make inferences about objects. For example, if I classify the drink in my glass as an alcoholic beverage, I am more likely to make assumptions about how many I can drink and what I will feel like afterwords.
For years psychologists and philosophers have wrestled with the question of how people categorise objects or situations. How do they decide that a crab is not a spider for example? One possibility is that people compare the features of objects with a list of defining features – qualities that are essential, or necessarily present, in order to classify the object as a member of the category. For example: spiders are usually a dark brown or black colour, covered in fur, have a big abdomen and can crawl in any direction, while crabs are usualy orange or red in colour, have a hairless shell, have a plate shaped body and can only crawl sideways – and they have pincers! These defining features ensure that we never confuse a crab for a spider. These are well-defined concepts – they have properties clearly setting them apart from other concepts.
Most of the concepts used in daily life, however, are not easily defined. Consider the concept good. This concept takes on different meanings when applied to a meal or a person: very few of us look for tastiness in humans, and sensitivity in a meal. Similarly, the concept adult is hard to define, at least in Western cultures: at what point does a person stop being an adolescent and become an adult? Is it when they reach a certain age, or when they realise a certain quality in their behaviour?
People tend to classify objects rapidly by judging their similarity to concepts stored in memory, this is the reason why a person would almost instantly recognise a parrot or a pigeon as a bird, but might take longer to recognise a penguin as a bird. People classify in this way by referring to a prototype, which is basically an outline of an object used to compare all other object in the same category. For example, when people construct a prototype in their minds about birds, the image is not necessarily of any bird in particular, but rather a rough sketch contains all of the defining features (shape, size and colour etc).
Hierarchies of Concepts – Many concepts are hierarchically ordered, with further sub categories branching off from the main ones. Efficient thinking requires choosing the right level of category on the hierarchy. A woman walking down the street in a bright yellow raincoat belongs to the category mammal, and human, just as clearly as she belongs to the sub category woman. We are more likely to say ‘Look at that woman in the yellow raincoat’ than ‘Look at that mammal in a brightly coloured artificial skin’.
The level people naturally tend to use in categorising objects is known as the basic level: the broadest, most inclusive level at which objects share common attributes that are distinctive of the concept (for example: woman, car, cat, dog, house). The basic level is the level at which people categorise most quickly, which is why it is natural to gravitate towards using it.
At times, however, people categorise at the subordinate level, the level of categorisation below the basic level in which more specific attributes are shared by members of a category. This is the level where people distinguish between objects that fall under the basic category, for example a bird watcher will distinguish between a blue bird and a hummingbird.
People also sometimes classify objects at a superordinate level, which is an abstract level in which members of a category share few common features. A farmer, for example, may ask, ‘are the animals in the barn?’ rather than list all of the animals that should be in the barn. The superordinate level is one level more abstract than the basic level, and members of this class share fewer specific features.
The hierarchy can be more easily explained by looking at the above diagram, here it is visually apparent how the system works. In this example, mammals are classified as superordinate, dog is grouped at the basic level, while golden retriever, dalmation and siberian huskey (all different breeds of dog) are linked to the subordinate level.