An ideogram or ideograph (from Greek ἰδέα idéa "idea" and γράφω gráphō "to write") is a graphic symbol that represents an idea or concept, independent of any particular language, and specific words or phrases. Some ideograms are comprehensible only by familiarity with prior convention; others convey their meaning through pictorial resemblance to a physical object, and thus may also be referred to as pictograms.
The numerals and mathematical symbols are ideograms – 1 'one', 2 'two', + 'plus', = 'equals', and so on (compare the section "Mathematics" below). In English, the ampersand & is used for 'and' and (as in many languages) for Latin et (as in &c for et cetera), % for 'percent' ('per cent'), # for 'number' (or 'pound', among other meanings), § for 'section', $ for 'dollar', € for 'euro', £ for 'pound', ° for 'degree', @ for 'at', and so on. The reason they are ideograms rather than logograms is that they do not denote fixed morphemes: they can be read in many different languages, not just English. There is not always only a single way to read them and they are in some cases read as a complex phrase rather than a single word.
In proto-writing, used for inventories and the like, physical objects are represented by stylized or conventionalized pictures, or pictograms. For example, the pictorial Dongba symbols without Geba annotation cannot represent the Naxi language, but are used as a mnemonic for reciting oral literature. Some systems also use ideograms, symbols denoting abstract concepts.
The term "ideogram" is often used to describe symbols of writing systems such as Egyptian hieroglyphs, Sumerian cuneiform and Chinese characters. However, these symbols represent elements of a particular language, mostly words or morphemes (so that they are logograms), rather than objects or concepts. In these writing systems, a variety of strategies were employed in the design of logographic symbols. Pictographic symbols depict the object referred to by the word, such as an icon of a bull denoting the Semitic word ʾālep "ox". Some words denoting abstract concepts may be represented iconically, but most other words are represented using the rebus principle, borrowing a symbol for a similarly-sounding word. Later systems used selected symbols to represent the sounds of the language, for example the adaptation of the logogram for ʾālep "ox" as the letter aleph representing the initial sound of the word, a glottal stop.
Many signs in hieroglyphic as well as in cuneiform writing could be used either logographically or phonetically. For example, the Sumerian sign DIĜIR (𒀭) could represent the word diĝir 'deity', the god An or the word an 'sky'. The Akkadian counterpart could represent the Akkadian stem il- 'deity', the Akkadian word šamu 'sky', or the syllable an.
Although Chinese characters are logograms, two of the smaller classes in the traditional classification are ideographic in origin:
An example of ideograms is the collection of 50 signs developed in the 1970s by the American Institute of Graphic Arts at the request of the US Department of Transportation. The system was initially used to mark airports and gradually became more widespread.
Mathematical symbols are a type of ideogram.
See also: Pasigraphy
Inspired by inaccurate early descriptions of Chinese and Japanese characters as ideograms, many Western thinkers have sought to design universal written languages, in which symbols denote concepts rather than words. An early proposal was An Essay towards a Real Character, and a Philosophical Language (1668) by John Wilkins. A recent example is the system of Blissymbols, which was devised by Charles K. Bliss in 1949 and currently includes over 2,000 symbols.