Lecture Notes: Peirce's "How to Make Our Ideas Clear"

UC Davis Philosophy 1

G. J. Mattey

Clear and Distinct Conceptions

The logic books in Peirce's time considered the best conceptions of things to be those which are both clear and distinct. Descartes was responsible for the distinctions between the clear and the obscure, and the distinct and the confused. Descartes understood a clear conception is one which allows us to recognize its instances infallibly. If I have a clear conception of a flower, then I will be able to distinguish flowers from non-flowers whenever I am presented with any object. Peirce comments that given this definition, it is very rare that anyone has a clear conception, though such a thing would be good to have. Instead, what most of us have is conceptions that we are familiar with to the extent that we do not hesitate to use them. We can, and do, make many errors when operating with such a conception.

The logicians do not count a clear conception as the highest type , however. A conception that is both clear and distinct is said to be the best kind to have. Descartes seems to have thought that a distinct conception is one that survives all challenges posed against it. (We can only speculate about this, given that Descartes did not adequately define distinctness). Leibniz refined this notion by appealing to definition. A distinct conception is a clear conception whose definition contains nothing that is not clear. As Peirce notes, Leibniz took this to the extreme, as if we can learn everything there is to know about a thing from its definition.

A Priorism

What the accounts of clarity and distinctness by Descartes and Leibniz boil down to are, respectively, familiarity and abstract definition. Descartes had good reason to look to clarity and distinctness, as he was battling against the method of authority that had been prevelant in the Middle Ages. He substituted for the authority of the Church the authority of reason, adopting the a priori method. Our clear and distinct conceptions, according to him, are signs of what is "agreeable to reason." But although this transition was an advance, Descartes overlooked a key question: how do we distinguish between a conception that is clear and one that only seems to be so? Is the conception of God as a perfect being, for example, really as clear as Descartes thought it was? Leibniz thought that error could lurk in apparently clear conceptions, which is why he required that all the components of the definition be clear. But this only pushes the problem back. How do we distinguish between a clear component of a definition and a component that only seems to be clear?


Peirce now procedes to examine clarity and distinctness from a fresh perspective. The easiest way to obtain clear conceptions is to keep them meager and restricted. Any complexity introduced into our conceptions makes the likelihood of unclarity greater. Indeed, those people how have rich conceptions are mostly led astray by them. This is so especially of young people, who are attracted to them at a time when clearer conceptions would serve them much better, due to their inexperience. When they become intellectually mature, they may abandon their complex conceptions, but the resulting clarity is of less use to them at this point, because they have the experience they need to get along well in the world. The intellectual lives of many young people are ruined by their pursuit of unclear ideas. People go on vain quests to square the circle, for example, or unravel conceptions such as that of God.

Thought and Belief

The value of thinking, and thus of conception, is to yield belief. Peirce recounts his description of belief in the companion essay "The Fixation of Belief.". Doubt is a hesitancy, an irritant that stimulates the mind to investigation through thought. Belief is the settlement of doubt, thought at rest. So the goal of thought is to attain this state of rest. What makes doubt irritating is that it is a hindrance to action. It is thinking, resulting in belief, which overcomes this hindrance and allows us to act on the basis of a settled conception of things.


The tie between thought and action is very tight. We can in fact identify beliefs in terms of the actions which they would bring about. Two beliefs expressed in different sentences are the same if they are such as to produce the same action. Thus the meanings of the conceptions making up the beliefs are also understood by reference to action. Conceptions have different meanings insofar as they lead to different practices. What do we mean by our conception of wine? Only the effects that wine has on our senses. We can fix these effects in a definite way, and this in turn is what gives the conceptions the highest degree of clarity. This is a pragmatic conception of meaning: it is practical effects which defines the meanings of conceptions.

An Example: Freedom

A notoriously unclear concept is that of human freedom. Here is a case where freedom of action is at issue. I have done something of which I am ashamed. Could I have resisted the temptation that overcame me and not done the actions? Was I free to have done otherwise than what I did? This depends on the practical effects of the conception of freedom I am working with. I was free not to do what I did insofar I I can say that if I had willed not to do it, I would not have done it. But I was not free to do it insofar as I was unable to overcome the irresistible temptation that I had. So we in fact have two different conceptions of freedom, associated with two different sets of practical effects.

An Example: Force

The pragmatic criterion of clarity applies to scientific as well as metaphysical conceptions. What is force? Philosophers have distinguished between force as acceleration and as the cause of acceleration (which may be unknown). Newton claimed that we know that force exists through the phenomenon of acceleration but not what force is in itself. Peirce counters that there is no practical difference between these conceptions. If one knows the accelerations and the laws of motion governing them, we know all there is to know about force. There would be no practical effect of knowing "the cause" of the acceleration.


A metaphysical conception that has always been far from clear is that of reality. Peirce applies his progressive analysis of clarity to this conception. The first grade of clarity is that of familiarity. In this sense, the conception of reality is as clear as can be, as even a child's conception is clear in this sense. The second grade of clarity is that of distinctness. We can give a definition of reality of this sort: the real is that whose characteristics are independent of what any individual thinks them to be. There is nothing wrong with this as an abstract definition, but how does it apply to our actual designation of objects as real? The answer is that it does so only in practice. This is the third and highest grade of clarity. The real is that which is destined to be agreed upon by all investigators. This is not to say that reality means that upon which all investigators will agree, but agreement is the practical test of the conception and the only way we can bring it to the utmost clarity.

Ideal Agreement

It may be thought that there is a conflict between the criteria of distinctness and of practice. The distinct conception of reality is of that which is independent of what anyone thinks, but the practical criterion appeals to what people do think, to what they agree upon. But there is no conflict here. In the first place, the definition of the real must be understood in terms of what individuals (you, I, or some other person) think. It does not exclude a connection to what everyone would think if they were to investigate the matter. Thus the practical criterion is not one appealing to actual agreement, but to an ideal agreement. Here it would seem that we find another obstacle to clarity. How can we know what everyone would agree upon were they to conduct investigation? Perhaps we do not know what ultimately is real. But we at least have a clear conception of what reality is through the practical criterion.

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