The Problem of Knowledge – Part 7: Kinds of Ideas



  • Ideas According to Their Origin
  • Ideas According to Their Relations
  • Ideas According to Their Comprehension
  • Ideas According to Their Extension


Ideas can be looked at from different viewpoints and categorized in different ways. We need to have a comprehensive understanding of the idea and how different kinds of ideas function.

Ideas According to Their Origin

Ideas from the viewpoint of origin can be said to be intuitive and immediate or abstractive and mediate.

Ideas According to Their Origin
Intuitive and Immediate
Abstractive and Mediate

Intuitive or immediate ideas are those which are formed as the result of the direct perception of things. As we experience our world our senses are constantly providing us with sense data. We see objects of all sorts along with their colors, sounds, smells, textures, and tastes. All these things make an impression on our senses. The senses send these messages to the mind and our intellects form ideas of these things as we perceive them.

But that is not all. At the same time we can turn our attention to the mind itself and watch it form ideas of these things. The intellect also forms ideas of our minds and its workings because it can perceive directly its own functioning. We can, therefore, perceive two worlds around us&emdash;the physical world we experience through our senses and the world of thought within us.

All ideas formed of immediately present objects which we perceive as present to us are called intuitive ideas.

Abstractive or mediate ideas are formed of objects by some means other than their immediate perception. For example, we form ideas of places, persons, and things through reading, watching television, and conversing with other people. We also experience things like heat from our furnace and light from our lamp which we know are the result of electricity. We have an idea of electricity even though we don’t perceive electricity itself but only its effects.

All ideas formed through deduction, through a processing of reasoning, or through a knowledge of some other thing, are abstractive or mediate ideas.

Ideas According to Their Relations

As far as their mutual relations are concerned, ideas can be either connex or disparate.

Ideas According to Their Relations

Ideas are connex when one idea necessarily includes or excludes the other.

Examples of connex ideas which include each other are: mother-child, husband-wife, superior-inferior, teacher-student, employer-employee, politician-constituent.

Examples of connex ideas which exclude each other are: day-night, virtue-vice, good-bad, rich-poor, tall-short.

Ideas are disparate when they neither necessarily include nor necessarily exclude each other.

Examples of disparate ideas are: man-black, wise-good, wheel-wood, rich-famous, tall-handsome.

A man may be black, but some men are not. A wise person may be good, but some are not. A wheel may be made of wood, but it need not be. A person may be rich and unknown, or famous and poor. A man may be tall, but he need not be handsome (although he may be).

As far as their mutual relations are concerned, ideas can be either identical or diverse.

Ideas According to Their Relations

Ideas are identical when their comprehension is the same.

Examples of identical ideas are: human being-rational animal, salt-sodium chloride, dog-sentient living substance, water-two atoms of hydrogen with one atom of oxygen (H2O).

Ideas are diverse when their comprehension is different.

Examples of diverse ideas are: human being-automobile, dog-water lily, house-whale, gold-ruby.

Furthermore, diverse ideas can be compatible or incompatible.

Diverse Ideas

They are compatible when the attributes of the comprehension of both can be united into another or third idea.

Examples of compatible diverse ideas are: man and black may be united to form the idea “black man.” Rich and famous may be united to form the idea “a rich, famous man.”

They are incompatible when the comprehension of one idea excludes the attributes of the other.

Examples of incompatible diverse ideas are: virtue-vice, good-bad, light-dark, green-purple.

The foundation for the incompatibility of ideas is called the repugnance of ideas and may be of different kinds. There are four:

  • Contradictory ideas are two ideas of which one expresses the simple denial of the comprehension of the other. Examples would be: living-nonliving, good-not good, being-nonbeing, equal-unequal.
  • Privative ideas are two ideas of which one signifies a perfection and the other denies a perfection in a subject which naturally ought to have it. Examples include: living-dead, healthy-diseased, sanity-insanity, sight-blindness.

We need to note here the importance of the word “naturally.” A rock, for example, is not supposed to have life and therefore cannot be said to be dead. It is merely “lifeless.” Trees are not “blind” because they are not supposed to have sight. They are “sightless.” The idea of “privative” does not apply in cases where the subject should not naturally possess the attribute. There is, then, a middle ground in some cases: life-lifeless-dead, sight-sightless-blind.

  • Contrary ideas represent the two extremes among objects of a series belonging to the same class. Examples of such ideas are: white-black in the class of colors, wise-foolish in the class of conduct, happy-miserable in the class of emotion, hot-cold in the class of temperature.

Contraries are mutually exclusive and cannot be true at the same time in the same subject. Between contraries, however, there is a middle ground and both contraries may be false at the same time. Contraries always presuppose a series wherein there are intermediate stages between one extreme and the other. Hot and cold in the class of temperature, for instance, represent the extremes between which there are various gradations of warmth.

  • Relative ideas are two incompatible ideas united in such a way that the one cannot be understood without the other.

For example, take the ideas of mother and child. These two ideas are mutually incompatible and exclusive. If you are the mother, you can’t be the child. Now, of course, you are the child of your mother, but that is another and different relationship and is not applicable. But you cannot be the mother and the child within the same relationship at the same time. In other words, you can’t be your own grandpa! More examples would be: master-servant, cause-effect, east-west, left-right.

A knowledge of the difference among contradictory, privative, contrary, and relative ideas is important because if we are certain of the truth of a statement containing one incompatible idea, we are equally certain of the falsity of the opposite statement.

Ideas According to Their Comprehension

Let’s take a look now at ideas from the viewpoint of their comprehension.

Ideas may be simple. This means their comprehension consists of one single element or attribute. Examples of simple ideas are “being,” “one,” and “object.” Their comprehension consists of a single attribute or element.

Ideas may be composite. This means their comprehension consists of more than one element or attribute. Most ideas we have experience with are composite. Ideas such as house, animal, billionaire, plumber, child, and so forth are composed of a number of attributes or elements. Recall that the idea of “human being” is composed of substance, body, living, sentient, rational.

Some ideas are concrete. These ideas express a nature or determining element as inherent in a subject. A concrete idea always represents an object as it is found in reality. Examples of concrete ideas are: horses, man, lilies, herons, salmon. These are things in nature. Other examples are black, blue, sharp, tall, small. These ideas represent attributes of things in nature.

Some ideas are abstract. These ideas express a nature or determining element considered by the mind as separated from the subject in which it inheres. The concrete idea of “man” becomes an abstract idea when we consider it by itself as “humanity.” “Horse” is a concrete idea but “horseness” is an abstract idea. “Black” is a concrete idea but “blackness” is abstract, as are “sharpness,” “tallness,” and “smallness.”

Ideas From Their Comprehension


Ideas According to Their Extension

From the viewpoint of extension, ideas may be singular, universal, particular, or collective.

Ideas are singular when they represent a single object only. Examples are: Thomas Jefferson, my dog Ming, Socrates. These are known as proper nouns or names in English. But ideas can also be singular if the class name is such that it can apply to only one object. For example: “this hat” is singular because there can only be one hat in the class of “this hat.” Also, “the President of the United States” is a singular idea because there is only one individual within the class.

Ideas are universal when they represent some common nature or element which can be applied to a class as a whole and to each individual member of that class. The great majority of ordinary ideas are universal ideas. The idea of “human being” fits every human being, past, present, and future. The statement “The dog is an animal” is as true of my Lhasa Apso, Ming, as it is of all the dogs that have ever lived or will live.

Ideas are particular when they are universals taken partly and indeterminately. The singular idea applies to only one individual. The universal idea applies to each and all of a class. The particular idea, on the other hand, applies neither to one nor to all, but to some of class in an indeterminate manner.

If we can place the word “all” or “every” before an idea, it is universal. But if we place the word “some” before an idea, it is particular. For example: “Human beings are mortal” is the same as “All human beings are mortal.” In this case, “human beings” is a universal.

If we say “Some human beings are black,” we restrict the universal idea “human beings” to an indeterminate portion of the whole class of human beings and we then have a particular idea. While “human being” may be universal in some statements, we can make it particular in other statements by restricting its application only to “some.”

Again, we have the possibility of a confusion here. This is because of our customary use of ordinary language; a point that has been made before. Recall the statement about Dutchmen: “Dutchmen are stubborn.” What is meant? All Dutchmen (universal idea) or just some Dutchmen (particular idea)? In deciding whether an idea is to be taken in a universal or particular sense, we must consider the usage of language and the context in which the idea appears.

How many useless arguments have taken place because it was not determined whether an idea was to be taken as a universal or as a particular?
A collective idea is one that applies to all the individuals as a class but not to the single individual member of the class. Think of the ideas “army,” “troop,” “herd,” “company,” and “flock.” The idea “army” can be applied to all the soldiers taken as a class but no individual member is considered an army. A goose might be a member of a “flock” but it is not a “flock” itself.

But be aware. Consider the statement “A library is a collection of books.” “Book” is a universal idea because the idea applies to each and every book in the library. But “library” is a collective idea because it can only be used of all the books taken together and does not apply to the single books as such.

Singular, universal, particular, and collective ideas are important in arguments and we should clearly understand the differences among them. The universal ideas, however, are of most importance and we will discuss them in more detail next.

Ideas From Their Extension

Dr. Jonathan Dolhenty was the Founder and President of The Center for Applied Philosophy and the Radical Academy, and is Honorary Philosophy Editor at Self-Educated American. Self-Educated American has adopted these projects beginning with a republishing and preserving of all of Dr. Dolhenty’s work.

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