Plato’s Divided Line

Using a line for illustration, Plato divides human knowledge into four grades or levels, differing in their degree of clarity and truth. First, imagine a line divided into two sections of unequal length (Figure 1, hash mark C). The upper level corresponds to Knowledge, and is the realm of Intellect. The lower level corresponds to Opinion, and concerns the world of sensory experience. Plato says only that the sections are of “unequal” length, but the conventional view is that the Knowledge section is the longer one.

Then bisect each of these sections (hash marks B and D). This produces four line segments, corresponding to four cognitive states and/or modes of thinking. From highest to lowest, these are:

  • noesis (immediate intuition, apprehension, or mental ‘seeing’ of principles)
  • dianoia (discursive thought)
  • pistis (belief or confidence)
  • eikasia (delusion or sheer conjecture)


Figure 1. The Divided Line


  • Plato admits to being loose with terms. For example, while noesis mainly refers to the highest of the four cognitive states, sometimes he uses it to denote the intellectual sphere generally. Also, he sometimes calls the highest grade episteme, but also uses that term in a more general sense to refer to technical sciences.


  • In any case, it is evident that these four states correspond to the stages of prisoners’ ascent in the Cave Allegory.


  • The line image lets Plato point out instructive ratios concerning truth quality amongst the states. Specifically:


    1. As Being is to becoming, so Knowledge is to Opinion.
    2. As Knowledge is to Opinion, so noesis is to pistis,
    3. And dianoia is to eikasia,
    4. And (though Plato does not say this explicitly, but rather lets us see it ourselves) noesis is to dianoia.


Plato certainly placed the Divided Line in the center of the Republic for a reason. Thus we must begin by understanding what the nature and purpose of the Republic is. To facilitate inquiry we will make the following assumptions:


  1. The Republic is mainly an ethical and psychological work. That is, we accept the view expressed by Hoerber (1944), Guthrie (1986), Waterfield (1993), Annas (1999), Blössner (2007) and others that any interest Plato may have had within the work in actual civil government is secondary and subordinate to his psychological and ethical interests. As Socrates states explicitly in 2.368d–2.369a and reminds us frequently, the ideal City-State is presented as a conceptual tool that enables us to better understand our own inner, psychic life.


  2. The model works because the human psyche may indeed be accurately likened to a commonwealth of citizens. Such psychic pluralism is recognized by dozens of modern theories of human personality (for reviews see Lester 1995, 2007; Rowan, 1990; Schwartz, 1995). Different theories give different names for these personality elements, but overall the terms subpersonalities or sub-egos seem adequate, at least if understood very generally.

    We have, in short, a separate subpersonality or sub-ego associated with every one of our social roles and relationships, jobs and projects, goals, hopes, plans and ambitions, appetites and desires, passions and emotions, dispositions and inner voices, styles, self-images and self-concepts. And these are only our conscious elements. Who knows how many more ‘people’ there are within us operating at an entirely sub- or unconscious level!


  3. The commonwealth of our psyche — psychopolis — can well or poorly governed, congenial or conflict-ridden, integrated or fragmented, harmonious or discordant. Plato’s aim in the Republic — identical with his and Socrates’ overall project — is to instruct us how to achieve a well-governed, harmonious psyche by means of philosophia, the love of Wisdom.


  4. A distinctive and important feature of the Platonic/Socratic system is that ethics and epistemology are inseparable. In an oppressive, conflicted soul-city, each subpersonality seeks only its own narrow interests. In the ideal soul-city each subpersonality looks to the good of all. For example, in a vicious soul-city, the money subpersonality may seek to acquire wealth by questionable means, putting it into conflict with other subpersonalities. Harmony of the soul-city (personality integration) is accomplished when subpersonalities instead seek direction from a higher source — a separate faculty (or faculties?) concerned with Wisdom, noesis, higher intuition, inspiration, etc., and a justice which benefits the entire self-community


  5. The Republic must offer sound practical advice for our daily mental life, or it would not be so singularly admired and acclaimed. Its aim is to teach us how to think and how to live.
Salvation from Egoism by Higher Knowledge

Now let’s try to put the pieces together. To begin, we are probably on solid ground to suggest that the Divided Line is principally concerned with moral epistemology: how do we know what to do (i.e., what is best for us), both in general and at any given moment? Upon the answer to this eminently practical question all our well-being depends. It is true that Plato includes mathematical examples in the Divided Line. But this doesn’t mean he’s spliced in an investigation of mathematical or scientific epistemology amidst his great work on personal ethics. It’s more plausible to see these as examples drawn from a fairly explicit domain (mathematics) to illustrate corresponding aspects of a less clear one (moral experience).

If we accept this view then what Plato seems to be saying in the Divided Line is that there is a special form of knowledge, noesis, which is a much better basis for guiding our thoughts and actions than other, lesser forms of knowledge. It takes little sophistication to recognize that noesis is better than the more degenerate kinds of ‘knowing’ — i.e., the eikasia and pistis displayed by prisoners of the Cave. What is far more subtle and interesting, and what is therefore perhaps more important for Plato here, is the contrast between dianoia, ordinary discursive ratiocination, and noesis.

This distinction is vital. While dianoia thinking certainly has benefits, we have a distinct tendency to over-rely on it and to forget its limitations. The weakness of dianoia is that it must begin by taking as true unproven assumptions. We are, in effect, presupposing a model of reality before we begin our deliberations. But any model, be it logical, geometrical, or moral, is only imperfect. Its conclusions may be, and frequently are, wrong. Our selection of assumptions, moreover, is bound to be influenced by our passions and prejudices. Our dianoia thinking tends to reflect the values and prejudices of whatever subpersonality is currently activated. We then see reality partly — through a glass darkly. Moreover, the principle of cognitive dissonance may cause us to ignore, distort, or rationalize away any data which do not fit our preconceived model.

In contrast, noesis presupposes a soul that has turned away from specific selfish concerns to seek the Good itself. With this change in mental orientation — this Pauline metanoia or Plotinian epistrophe — we may then begin to see things more truly, and in their proper relation to one another. We may better think, judge — and therefore act — according to natural law and right reason. We will consequently be more harmonized with the external world as well as within ourselves.

Noesis (Peters, 1967, 121ff.) is the mental power or faculty associated with an immediate apprehension of first principles (Forms) of mathematics, logic, morals, religion, and perhaps other things. So understood, noesis, when concerned with moral Forms, is very close to, if not the same thing as what is traditionally called Conscience. By Conscience we mean not a Freudian super-ego formed by the internalization of arbitrary social conventions, but an innate sense, something divine, and something perhaps closely associated with consciousness itself (let us not forget that in some languages, such as French, the same word denotes both consciousness and Conscience.) We need not commit ourselves to a particular religious creed to say that this moral noetic sense is a phenomenological reality — a clarifying, integrating, joyful, loving faculty of human consciousness.

The characteristic human flaw of turning away from the Good — and instead relying on our own fallible substitutes for divine Wisdom — is hubris, the fundamental sin against which Greek philosophy and literature so forcefully and persistently warns us. This great concern of Homer, Hesiod, and the tragic poets is also Plato’s.


As Plato explains in Book 7 (7.532e ff.), it is by dialectic that we rise from the cave of ignorance to noesis. By dialectic the eye of the soul, which, as in the Orphic myth, is otherwise buried in a slough of mud, is by her gentle aid lifted upwards (7.533c-d).

For Plato, dialectic is more than logical analysis. It is a focusing of ones attention and intentions on the search for and reconnection with Truth. It coincides with a turning away from sensual pleasure as the organizing principle of ones thought life.

In a broad sense dialectic might include any activity by which, through the exertion of one’s intellect and will, greater mental sharpness occurs. Plato does seem to suggest that this mental ability can be improved by the study of mathematics (and also of music, gymnastics, and astronomy — or whatever these serve as allegories for in Book 7).

Dialectic is a topic of central importance to Plato, and he also discusses it throughout his other dialogues (e.g., MenoParmenidesPhaedoPhaedrusPhilebusSophistStatesman, and Theaetetus).

The late Neoplatonist, Proclus, in a famous passage of his commentary on the Parmenides, describes three different forms — or, as he calls them energies — of dialectic: (1) arguing both sides of an issue; (2) trying to uncover truth; and (3) refutation of a false view (In Parm. 653; Morrow & Dillon, p. 43f; cf. section 989).

Specific Platonic/Socratic techniques for the second of Proclus’ categories include collection (gathering together of similar examples), division (seeking principles which distinguish some examples from others), and the method of hypothesis (exploring the implications of a hypothesis). For further details see Benson (2010), Kinney (1983), Robinson (1953), etc.

Note that the very effort to define dialectic and discover its essence is a form of dialectic.

Platonic Ascents

In his dialogues Plato presents three methods of ascent to the Good (see Plotinus, Enneads 1.3). In the Republic there is the ascent of dialectic. In the Symposium, there is the famous ascent by Love of Beauty. The Phaedrus, especially in the Chariot Allegory, describes the ascent by Moral Virtue (harmonia). These three methods first ascend to the second-highest tier of Forms: Truth, Beauty, and Justice, respectively. One may then ascend higher to their common essence, the Form of the Good, or Goodness itself.

Are there other avenues? Plato’s emphasis on just these three certainly doesn’t rule out the existence of more. Could prayer and religious ritual, for example, comprise another? What about yoga? Communing with nature? The practice of charity?

Before proceeding to final discussion let us summarize our observations thus far in the form of Table 1.

Table 1. The Divided Line

Level (highest to lowest)NameMeaningCave AllegoryExample
1noesisHigher Reason; direct apprehension or intuition of moral, logical, relational, or religious first principlesoutside cave, seeing Forms (e.g., direct apprehension of moral truths)seeing another person in the light of spiritually-based compassion
2dianoiadiscursive thought; ratiocination; lower reasonoutside cave, seeing images of Forms (e.g., verbal, conceptual representations of moral truths)logical acceptance of truth that one should treat another person with compassion
3pistisplausible opinion; trust; confidenceseeing objects in cave (e.g., egoistic distortion of a moral concept)noticing a person’s faults instead of their virtues and goodness (selective, egoistic perception)
4eikasiabaseless opinion; delusion; fantasy- or wishful-thinkingseeing only shadows on wall of cave (e.g., moral opinion fully detached from reality)imagining faults or attributing false motives (e.g., psychological projection) to another person


In this section we will make some observations and suggestions concerning the further study of Plato’s Divided Line and associated themes, especially as they relate to modern psychology. First, though, two observations of a more general nature are offered.

The first concerns Plato’s mysticism here. In the sense that Plato is suggesting modes of knowledge above discursive reasoning, then, by a broad definition at least, he could considered a mystic. He is, however, able to approach this mysticism rationally, so that what is being effected is an integration of our epistemological faculties. In any case, it is important to see that what Plato offers is a practical mysticism of everyday life — something that enriches our ‘ordinary’ experience. He is not merely presenting an ascetical, otherworldly life of pure contemplation, suitable only for a monastic existence.

The second general point is that we have here at best only scratched the surface of the Divided Line. In 7.534 Plato explicitly alludes to there being other categories of opinion and knowledge, such as would require a discussion many times longer to flesh out. Perhaps, however, he’s supplied some clues in 7.516 when he alludes to the prisoner newly emerged from the cave only being able to see the Sun (i.e., the Form of the Good) after preliminary stages of seeing, in order, shadows and reflections of objects, objects, the light of the moon, stars, and heavens, and the light of the Sun.

Maslow’s Being-psychology

Some possible connections between Platonic philosophy and the Being-psychology of the influential humanistic psychologist Abraham Maslow (1968; 1971) should be noted.

Maslow argued that once human beings meet their basic life necessities their attention turns naturally to higher things — to what Maslow called growth (as opposed to deficiency) motivation and Being (as opposed to becoming) experience. Associated with this higher life are certain intense but brief peak experiences, and somewhat more durable, if less powerful plateau experiences. These superior states of consciousness, which most people experience to some extent, are characterized by such things as enhanced clarity of perception, a feeling of deeper meaning, truth, and completeness of experience, a sense of timelessness, egolessness, sacredness, innocence, and absence of negative thoughts and emotions. Just as in peak or plateau experience our external vision may suddenly come into greater focus, revealing more depth, detail, and beauty, so may our inner moral, intellectual, and philosophical vision. In sum, these states are perhaps as close to pure happiness and wisdom as any we can identify.

For Maslow, in such states it feels as though we are perceiving true reality, eternal verities — Being. In contrast, our usual modes of perception and consciousness allow us only to experience the transitory realm of becoming. Maslow’s language clearly alludes to the Being-becoming distinction in Platonism — a distinction nowhere more explicitly presented than in the Republic. Nevertheless, Maslow is muted in his explicit enthusiasm for Plato, and perhaps for at two reasons. First, Maslow was a committed materialist and atheist, and this constrained how much of Plato, a theist, his theories could accommodate. Second, if Maslow had explored in more detail the implications of Platonism, his audience would likely not have cared. At the time of Maslow’s peak influence (the 1960’s and early 70’s), Plato had long since been banished from the university. Free-spiritism was the zeitgeist. The last thing people were interested in was Plato, the very symbol, in their minds, of obsolete and oppressive Western values and moralism.

Nevertheless the times have changed, and the inevitable engagement of modern humanistic psychology with Plato should not be put off longer. The entire positive psychology movement, of which Maslow is arguably the founder, or at least a major forerunner and influence, lacks two things which Platonism can supply: (1) a moral focus: a recognition that man is a moral being and that upon his moral life all his happiness depends; and (2) a plausible theory of epistemology that admits knowledge higher than rationalism. Without these, the success of positive psychology is questionable.

Brain Hemisphere Specialization and Integration

McGilchrist (2009, 2012) has recently recalled to our collective scientific attention the issue of lateralization of brain function, an important topic which laid strangely dormant for several decades. The basic premises of this work as relates to our discussion are as follows:

  • There is a marked asymmetry in function (and anatomy) between the left and right hemispheres of the human brain.
  • The left brain hemisphere (for the typical right-handed person) is more specialized for logical, linear thinking, focused attention, and certain verbal skills.
  • As human technology and language have progressed in recent centuries and millennia, the ‘left brain’ has become increasingly dominant.
  • This has thrown our brains, as well as our culture generally, into a state of conflict and disequilibrium. We need to learn to reintegrate or reharmonize our brain hemispheres.

A further important hypothesis of McGilchrist is that there is a definite connection between left-brain dominance and egoism. This is the meaning of the title, The Master and His Emissary, which alludes to a parable of Nietzsche. The proper role of our rational ego is to serve as the emissary, steward, or chief executive officer for the much larger organism, the Self. But the ego habitually oversteps its proper bounds, producing myriad problems.

Translated to the Divided Line, McGilchrist’s left-brain ego would seem to correspond reasonably well to dianoia-dominated thinking and morality. Plato, in teaching us about noesis, and perhaps drawing from a store of cultural wisdom deposited before modern rationalism took over, is then in a sense helping us to re-harmonize the audacious left brain with the rest of the psyche.

There is a limit to how closely we can map McGilchrist’s bicameral model of the brain to Plato’s tri-partite psychology. Further, all agree that the ‘two-brain’ model is more than a little oversimplified. Nevertheless, the work of McGilchrist and others offers some hope that there are identifiable neurophysiological correlates of the kind of moral and cognitive egoism (and its remedies) that Plato is concerned with.