The Index and the Icon

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Charles Sanders Peirce (1839-1914) was an early semiotician. His work was based on the pursuit of scientific and logical truth, and he developed his semiotics by using graphical representations (drawings and sketches). In discussing the kinds of relations that exist visually between signs and their objects, he noted three categories:

  • an index – a reference to reality, including constituent parts of the image.
  • a symbol – a conventionalised representation of a thing, either real or imaginary.
  • an icon – the likeness of or relationship to the subject in the image.

These ideas were introduced in his 1868 paper to the American Academy of Arts and Sciences.

A reference to a ground may also be such that it cannot be prescinded from a reference to an interpretant. In this case it may be termed an imputed quality. If the reference of a relate to its ground can be prescinded from reference to an interpretant, its relation to its correlate is a mere concurrence or community in the possession of a quality, and therefore the reference to a correlate can be prescinded from reference to an interpretant.

It follows that there are three kinds of representations.

First. Those whose relation to their objects is a mere community in some quality, and these representations may be termed Likenesses. 

Second. Those whose relation to their objects consists in a correspondence in fact, and these may be termed Indices or Signs.

Third. Those the ground of whose relation to their objects is an imputed character, which are the same as general signs, and these may be termed Symbols’. (Peirce, 1868, Sec. 14).

Signs and symbols are graphical presentations, and in everyday uses we often interchange them. Philosophically, signs are languages and are used in a communication system. Signs are considered broader than symbols, which are less a language and more an individual representation of a ‘thing’. Peirce noted that Signs include Indices, Symbols and Icons, which always puts them in a relationship with each other. (Buchler, 1955: 107).

For Peirce, an index is:

‘... a sign, or representation, which refers to its object not so much because of any similarity or analogy with it, nor because it is associated with general characters which that object happens to possess, as because it is in dynamical (including spatial) connection both with the individual object, on the one hand, and with the senses or memory of the person for whom it serves as a sign, on the other hand‘. (Buchler, 1955: 107).

So an index is as much about the viewer’s sensory perception of it as it is about its physical reality.

On the icon, Peirce commented:

It may be questioned whether all icons are likenesses or not. For example, if a drunken man is exhibited in order to show, by contrast, the excellence of temperance, this is certainly an icon, but whether it is a likeness or not may be doubted‘. (Buchler, 1955: 107).

In this sense, Peirce’s ‘icon’ is not just a likeness of a physical referent but could also be a relationship with a concept.

Peirce’s aim was to create a logical, self-contained theory of signs, and photography was a special case of that theory, where the image was created via a physical trace.

Today, in vernacular (and indeed dictionary definition from the Greek eikōn) use, we refer not only to an icon’s likeness, but also to an icon’s historical or cultural importance, possibly even veneration. This goes beyond simple representation of a subject or its relationship to it, to our subjective view of it.

For example, this is an icon, in everyday language, as a representation of the Madonna and child, and as an object of veneration.

Russia, 17th Century Virgin of Smolensk.

Walter Benjamin‘s commented about such ‘cultic artwork’. He suggested that photography cannot have ‘aura’, with the possible exception of portraits, because of mechanical reproduction. This implies that photography, without aura, cannot truly be ‘art’ (or cultic, iconic?).

That said, in everyday parlance, we elevate both paintings and photographs to iconic status. From Wittgenstein’s viewpoint, the use of words in everyday language is often more useful than a theoretical definition – hence ‘iconic’ in vernacular use means historically, culturally or socially important work rather than simply photographically representational. When we are debating, if we followed Wittgenstein’s advice, we should ask ‘Are we talking about the same thing?’

The meaning of a word is its use in the language‘. (Philosophical Investigations, Sec. 43, pg. 20).

I would thus propose that being iconic suggests that the viewer elevates the image to a deeper, more meaningful, emotional or psychological level in their critical appreciation of it than a simple representation.

Peirce’s interpretation of ‘indexical’ as requiring a physical referent (in the sense of Barthes et al) implies that a painting cannot be indexical, as there is no causal relationship in the way that there is with a photograph, light imprinting a sensitive surface. However other readings of Peirce’s text pick up on the more conceptual possibility, rather than a purely physical referent.

There is a strongly bifurcated aspect to Peirce’s definition, which is somewhat confusing: The former example refers to traces, physical imprints from one item to another. The latter has an important nuance that includes not necessarily physically contiguous references‘. (Schofield, Dörk and Dade-Robertson, pg 20).

Our MA program chooses to focus on the physical referent aspect of indexicality. It is about causal ‘traces’ of reality, although it is always mechanically interpreted by the camera and under the influence of the photographer. As Steph Cosgrove noted in ‘The Index and the Icon‘:

 ‘The perception of a special relationship between photography and the real world around us, was important to modernists as a unique quality of the medium‘. 

And, from ‘Is it Really Real‘:

‘Iconic characteristics’ significance comes from the way they look like the subject [my emphasis] matter they represent. Indexical characteristics, is where there is a causal relationship with their subject [my emphasis] and as we have seen, this has a special significance for the way in which we perceive photographs’.

Yet Steph goes on to say, from Batchen, that:

Photography may authenticate the existence of a scene at some point in time but cannot be relied on as an accurate and objective representation of it’.

In logical terms, referencing the real is thus a probability rather than a certainty. Is indexicality, therefore, even possible as a criterion for all photography? Further, Batchen also said of Peirce:

 ‘ .. those who look to Peirce for pragmatic evidence of an extra-photographic real (the “thing-itself ”), will, if they look closely enough, find in its place nothing but signs [my emphasis] … accordingly, if we follow Peirce to the letter … we must logically include the real as but one more form of the photographic [my emphasis]’. (Batchen, 2001: 142)

In other words, a photograph can never prove that something is real, it is only ever going to be a sign of something.

I have no issue with the physical referent being one way to consider the indexicality of photographs, and that is indeed legitimately the MA’s perogative. But I admit to finding it very ‘black and white’ versus paintings. Paintings are ‘made up’, in the sense that they are created over time, and often away from the actual scene. Photography tries to ‘capture’ what is actually there, at the moment of opening the shutter.

Using the second meaning of Peirce, noted above, paintings could also have ‘conceptual’ referents. Las Meninas, for example. In fact, it is quite possible that a painting (or sculpture) could do a better job of capturing the essence of some event, idea or person than a photographic image might.

Consider Delacroix’s Liberty, a truly iconic image, in a vernacular sense.

Eugène Delacroix. 1930. Liberty Leading the People.

This image is not indexical to a real event, yet it does refer to both an idea and a series of historical contexts. It also seems to find reflection in indexical photographs – Flag Raising over Iwo Jima, for example.

Jim Rosenthal. 1945. Flag Raising on Iwo Jima.

Not withstanding the fact that Rosenthal’s image was posed, so only tangentially  ‘true’ from a strict documentary perspective, I think it is an interesting question as to which image does more justice to the concept of freedom. I will leave the viewer to decide.

Yet, it is without question that both images are ‘iconic’ in their own ways, in both popular and critical imagination.

Stepping back, Pierce’s project was to provide a rational method to consider images.

Reasoning is dependent upon Graphical Signs. … By ‘graphical’ I mean capable of being written or drawn, so as to be spatially arranged‘. (Laja, 2000: 101).

Interestingly, portraits were of particular importance to him, much as they were to other, later writers, such as Benjamin, who saw aura in the work of Margaret Cameron. That would also seem to be a concept related to the engaging (iconic?) power of an image.

‘… portraits were among his preferred models of likeness, and they figure far more prominently to illustrate his category of icons than any other. Photographs, as products of a mechanical process, were indexical icons for Peirce‘. (Laja, 2000: 113).

E.H. Gombrich (1909-2001) later noted that:

We are used to making a clear distinction between two functions of the visual image – that of representation and that of symbolisation [my emphasis]. A painting may represent an object of the visible world, a woman holding a balance, or lion. It may also symbolise an idea. To those conversant with the conventional meanings attached to these images the woman with the balance will symbolise Justice, the lion Courage, or the British Empire, or any other concept conventionally linked in our symbolic lore with the King of Animals‘. (Gombrich, 1948: 31).

It would seem to me that photographs can rise to Gombrich’s classification.

Images can contain many signs and symbols. Nelson Goodman (1906-1998) wrote that ‘a symbol system is a symbol set correlated with a field of reference’ (Goodman, 1968: 6). Goodman’s project was to establish a formal, logical semantics and syntax by which we can visualise and understand our world.

In my undergrad days, I worked with the idea of logical congruence – defined when two things are in agreement, have harmony, conformity, or correspondence – but are not mathematically identical.

I examined how engineers can easily move from a artist’s sketch (of a building), to a working construction diagram, and eventually to an actual physical entity. I used electrical wiring diagrams to develop the idea, and it seems relevant to this MA task. How can we look at a photograph and really decide its indexicality?

Goodman commented that a symbol may or may not denote what it refers to, and that this denotation could thus have some form of truth value. In other words, its indexicality?

He also wrote that ‘green’ has a compliant, whilst ‘green horse’ has not. As an historical note: Goodman did not fully logically define these two varieties of compliant – the indexical versus the non-indexical sign – and that was the basis of my Final Paper.

Let me now use a real world example – the vacuum tube or diode.

A vacuum tube is a small tube from which all the air has been removed. The first vacuum tubes had just two elements, a heater (or filament) and a plate, and were called diodes. They rectified AC to DC. 

In 1907, De Forest invented the triode. He added a cathode which surrounded the filament. The cathode is heated by the filament and was a better source of electrons. He also added a control grid in the form of a spiral of wires or an open mesh (so the electrons can pass through) in between the cathode and plate. If the voltage applied to the control grid is lowered below that of the cathode, the amount of current from the cathode to the plate is reduced. To make an amplifier, a large positive voltage (several hundred volts) is applied to the plate through some sort of load. Then a signal is fed into the control grid. A relatively small amount of change in the grid voltage causes a much bigger change in the voltage across the load.


Let us unpack ways of considering the vacuum tube – as an index, as a symbol and as an icon.

1. Index

The diode was invited by John Ambrose Fleming about 1904. Its importance to modern electronics cannot be overstated. It provides a way of modifying electric current – in the first instance to change it from AC to DC. Here is an indexical, historical image of Fleming’s diodes.

Fleming’s Thermionic Diodes. 1919.

It seems clear that here a photograph is providing a completely indexical representation of the diode, with little room for subjective interpretation.

Turning now to symbols:

2. Symbol

The usefulness of a symbol, with real-world compliant or otherwise, is that it is removable from context, yet can also be associated with large sets of other symbols to create new meaning. The basic symbol for a diode in electrical wiring is this:

Vacuum Tube Diode

In and of itself, this has little utility – although an engineer, from their area of interest, would both recognise it and know how to use it. Put another way, in Barthes’ terms, the symbol itself has studium for some people. But the studium  becomes of even more interest when combined with other symbols. Here is a simple diagram of an amplification circuit, much as we would have in our homes.

In this context, the symbol for diode becomes a part of a logically well-formed diagram, where connecting real world items in the way depicted would indeed lead to amplification.

In the art world, perhaps the earliest master of signs and symbols was Paul Klee (1879-1940). He was never creating images with either an indexical truth, nor a suggested practical use. But he was abstracting the world into signs and symbols, creating his own visual language. His work is asking questions of the audience about what they are seeing, rather than pointing towards a certain meaning. It is a fascinating cross between Goodman’s compliant and non-compliant.

Klee’s symbols represent things that we might instinctively recognise, like a face, yet the whole is out of our reach, like a dream.

Paul Klee, 1939, Übermut Exubérance.

Photographically, we can make perhaps more logical sense of symbols, yet still provide new meaning.

Symbols are often used within an image, to add cultural context and meaning.

Consider Robert Franks’ Hoboken image.

Robert Frank. 1955. Hoboken, New Jersey.

The American flag is used as a powerful symbol, with two people in shadows, one partially hidden by the flag. A viewer will bring their own context and preconceptions to this image, although it is hard not to see that the flag seems to be more important than the people depicted.

Is that the reading that Frank intended?

Turning now to icons, I noted above that I find it helpful to consider how we use the word icon in everyday speech – as something or someone that has cultural, social, political or historical importance. . So how could that apply to the humble vacuum tube?


In the 1940s the invention of semiconductor devices made it possible to produce solid-state devices, which are smaller, more efficient, reliable and durable, and cheaper than thermionic tubes. So, scientifically the vacuum tube became yesterday’s technology, interesting historically but that is all.

However, when we buy Hi-Fi equipment today, some of the most expensive components are valve-driven amplifiers, with enthusiasts believing that they deliver better sound.

McIntosh Valve Amplifier

Thus, here is a totally indexical photograph of an iconic piece of technology (yours for just over £7000 today). Is this an iconic photograph? Hardly, it’s a high quality commercial representation of the amplifier. But it does depict, to a certain audience, an iconic product.

On the other hand, this is an iconic image, representing an entire era in American history and pivotal to any history of photography. Arguably most competent photographers today could take similar ‘indexical’ images – but it is unlikely that their work would become iconic. That has already been done.

Dorothea Lange. 1936. ‘Migrant Mother’.

This week, we have been asked about the truth that photography can offer us, and whether it is different to other forms of visual representation.

I hope that this short post suggests that photographs can offer truth, in ways that other plastic arts might not be able to.  Yet photography is also subject to the way that for centuries we have ‘decoded’ images.

I also suggest that we need more rigorous, logical use of language in discussing the essence of photography than is offered in many popular (canonical) works on the subject.

In particular, what do we mean by ‘congruence’ – how are the symbols in a photograph (or painting, for that matter) congruent with though not the same as the subject depicted? I believe that offers clues as to how we view and judge images today, whether as consumers of commercial images, or students of fine art.

Photographic congruence .. a future paper?


Header: Stefan Riepl. 2008. late Thermionic Vacuum Valves


BATCHEN, Geoffrey. 2001. Each Wild idea: Writing Photography History. 2002 Edition. Cambridge: MIT Press.

BENJAMIN, Walter. 1936. The Work of Art in the Age of Mechanical Reproduction. 2008 Edition. London: Penguin.

BUCHLER, Justus. 1955. Philosophical Writings of Peirce. New York: Dover. Available at (accessed 04/02/2019).

GOMBRICH, E.H. 1948. Icones Symbolicae: The Visual Image in Neo-Platonic Thought. Warburg Institute. Journal of the Warburg and Courtauld Institutes, Vol. 11 (1948), pp. 163-192. Available at: (accessed 08/02/2019).

GOMBRICH, E.H. 1950. The Story of Art. 12th Edition, 1972. London, Phaidon Press.

GOODMAN, Nelson. 1968. Languages of Art: An Approach to a Theory of Symbols. 1976 Edition. Indianapolis: Hackett Publishing Company.

LAJA, Michael. 2000. Pierce, Visuality and Art. University of California Press. Representations, No. 72 (Autumn, 2000), pp. 97-122. Available at: (accessed 08/02/2019).

PEIRCE, Charles Sanders. 1868. On a New List of Categories.  Proceedings of the American Academy of Arts and Sciences 7 (1868), 287-298. Available at: (accessed 08/02/2019).

SCHOFIELD, Tom, DÖRK, Marian and DADE-ROBERSTON, Martyn. Indexicality and Visualization: Exploring Analogies with Art, Cinema and Photography. Available at (accessed 08/02/2019).

WITTGENSTEIN, Ludwig. 1953. Philosophical Investigations. Trans. G.E.M. Anscombe. Oxford: Blackwell.

YATES, Mick. 1972. Criteria for Diagrammatic Truth. BA Finals. Leeds: University of Leeds.

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