On Aristotle's dialectical method

| 7th October 2019
The aims, scope and method of Aristotle's dialectic.



Dialectic is the same as rhetoric in that it is an intellectual activity aimed at changing minds, and is the same as logic in that it relies on reasoning to validate (or invalidate) arguments. It differs from rhetoric in that only logic should be deployed to persuade, and that it is aimed at a particular individual rather than a group, or a crowd. It differs from logic in that it is not concerned with the pursuit of absolute truth, or first principles, but in convincing a person of an argument. 

Read 'The nature of Aristotle's dialectic' here. 

Dr Evans explains that while dialectic is concerned with the individual and her perspective, logic is not: “Pure logic is not concerned with the vagaries of the individual's reaction, and indeed in its search for objectivity it is positively prohibited from considering the individual as such.” (75) He adds later: “Aristotle is aware that the conditions of the exercise of dialectical skill are such that, although the dialectician is indeed required to argue his case purely by logical means, he must at the same time not ignore the various ways in which circumstances which are external to his argument can affect its character.” (92) 


So what is the method of dialectic? Dialectic involves a dialogue between two people. These individuals do need an understanding of the logical method of reasoning - set out more fully here - and need to be seriously and genuinely engaged in the process. The concern is validating arguments on both sides. Dialectic is not a method for bad actors or the resolution of primarily emotional disputes. 

Aristotle asserts that dialectic does use logic to advance knowledge through the validation of arguments and through deductive reasoning through inference. “[W]e need to distinguish how many kinds of dialectical argument there are,” he writes in Topics. “One kind is induction, another is deduction. Here we discuss deduction, which is the essence of logic. 

The aim of both logic and dialectic is to validate the definition of things (indeed, everything from abstract concepts to physical objects). Logic seeks a true, absolute definition. Dialectic aims to validate or invalidate definitions presented in argument.

The beginning of any process of definition (of demonstration, and of argument) is actually very simple: we start with “this is the same is that,” and “this is different to that”: the human is the same as the bonobo in this way; the human is different to the bonono in this way. Dr Evans states: [T]here are certain things - same, other etc. - with which the dialectician is characteristically concerned...” (38). This is because ‘same’ and ‘different’ are the foundations of definition (of cognition and categorisation), which is how we come to recognise and define the things around us.

In both dialectic and logic, any one thing can only be defined by its relation to other things. The basic structure of a proposition includes a subject (the thing being defined) and an object (the thing it is defined in relation to) is. A proposition can be used as a premise in an argument, and through argument we can infer a new proposition, which is the conclusion. 


Dialectic and logic both arrive at definitions by identifying the unique properties that belong to the subject - the properties that really make it what it is as opposed to superfluous detail, which Aristotle calls the accidents.

For example, in a definition humans we would want to include language, but not necessarily fingernails. It is the use of language that differentiates humans from other apes. Both humans and apes have fingernails. Language is a unique property in this instance, fingernails are accidents. 

Dialectic, like logic, is concerned with propositions that include a subject and a predicate, and the relationship between the two. The subject is the thing that is defined in any proposition. The predicate is the object and the relation to that object that defines the subject. An example of such a statement is, “all humans are animals”.

Here, the human is the subject and animal the predicate. We know that those properties that are universal to animals (for example, the property of needing to eat to survive) will also be true for us humans. The object of the sentence - the animal - is used to describe the subject - the human. Both unique properties and accidents are predicates, but only the former is useful in establishing a higher level definition. 

To define something skillfully, we need to understand the wider class of things to which our subject belongs. This, in Aristotle’s terminology, is its genus. A genus is a class or category of things that share the same property. The genus ‘vehicle’ will include modes of transport including busses, cars and bicycles.

We then need to establish what properties distinguish it from the other things in its genus. These properties Aristotle calls differentia. The subject that is differentiated within a genus is the species (from specific). The bus is a public mode of transport used by many, the car a private use of transport used by a few.

The mode of ownership and use differentiates the specific car, and specific bus, which are both in the genus, or category, vehicle. Dr Evans states: “Aristotle argues that only if the definition contains the genus and the differentia, can it indicate the essence of the subject” (114). We define our subject by placing it into the correct place in a wider system of categories. 


A true definition of any subject states its essence: the essence is those properties that allow us to categorise it in its genus, and then differentiate it from other members of that genus. We arrive at the essence of any thing through this double-sided process of classification. This is why for Aristotle the pursuit of the essence of things is primary and paramount. As Dr Evans writes: “[T]he requirement that the definition indicate the essence is an unargued premiss to the discussion in Topics...elsewhere in Aristotle’s work the axiomatic character of this requirement can be seen.” (107). 

We can see here the influence of Aristotle’s interest in biology, and the natural world provides a useful range of things that can give us concrete examples of what we mean. Let’s begin with what is most familiar: ourselves.

Humans are a species. The species human belongs to the genus of ape. One of the many differences between humans and other animals is that we have a complex language. Therefore, through this double process of establishing our genus (the general group that we belong to) and our differentia (that which is specific to our species) we are able to develop a definition of human: an ape with language. This definition describes the essence of what it means to be human. 

The process of defining a thing through its genus and species is derived from, but not limited to, the practice of biology. We can use the same process to define concepts, such as “true” and “false”. These terms appear to be entirely the opposite of each other. However, both are concerned with the validity of whatever they happen to describe.

They belong to the genus of statements about validity. Yet the differentia is one is positive and one is negative. The definition of “true” is therefore “a positive statement about validity”. This provides us with the essence of what we mean by true. 


In dialectics, and in logic, when we define any object we are not required to fix the genus and the species. The choice we make depends on what exactly we are trying to define and - in dialectic - for whom.

For example, we can also say that all humans are systems. Here, we may be concerned about universal claims about all systems. These claims would logically be true of humans. The terms we chose in our propositions depend very much on what we are hoping to establish. With dialectics (but not logic) it also depends on the premises that we can agree with our interlocutor.

This process of establishing definitions and validating arguments is enhanced through the use of the syllogism. (A longer definition of syllogism is provided in this Endoxa article). In short, a syllogism is a method of arriving at (or inferring) a valid conclusion from two valid premises.

There is - Aristotle establishes - a particularly useful from of syllogism where the first premise states the general (or universal); the second states the specific (the individual) and the third the relationship between the two (the particular). The classic syllogism would look like this:

  1. All humans are animals

  2. Eve is a human

  3. Eve is an animal

If we agree that the premise that “all humans are animals” and also that “Eve is a human” then we can infer that the statement “Eve is an animal” is valid. This is the basis of formal logic. Dialectic uses the syllogism because it is compelling: it is highly likely to convince the person you are in conversation with, whereas logic utilises the same technique for slightly different purposes - the pursuit of absolute truth.

A sortie - a long chain of syllogisms - is the aim of rational thought. Aristotle argues in Topics: “[F]or it is impossible to demonstrate something if one does not start from the special foundations and link one's reasoning in a chain until one reaches what is at the end” (34/35).


This begs the question. What are these “special foundations”. For the syllogism, we need premises. Dialectic begins with “the securing of premises”. As we can see above, valid premises should provide us with valid conclusions, an invalid premise can conversely result in an invalid conclusion.

The house we build is only as sound as the foundations on which it sits. The securing of premises - according to Aristotle - includes 1. The detection of ambiguity; 2. The discovery of differences, and 3. The consideration of similarities. This follows tidily from our exploration of definition, above.

In this article I have attempted to give a brief definition and overview of Aristotle’s dialectic, setting out its aims, scope and method. Now that we have a working understanding of dialectic I want to follow Dr Evans in developing a dialectical definition of dialectic itself. This involves establishing the genus, or category, to which it belongs and setting out what properties define all the members of this category. Then I want to discuss how it is different to the other members of the category - it’s differentia. This will focus on the difference between dialectic and logic. 

The difference between dialectic and logic can be briefly and broadly explained by the fact logic (such as pure logic, formal logic) seeks absolute truth developed from true premises and sound argument, where dialectic seeks to persuade and calibrate arguments from the foundation of common sense.

Dialectic is therefore concerned with what people already understand, what is absolutely understandable, and how a person can guide her interlocutor from the first to the second position.

In the next article I will establish the essence of Aristotle’s dialectic.

This Author 

Brendan Montague is editor of The Ecologist. This article is part of the Endoxa.review project. 

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