Logograms are commonly known also as "ideograms" or "hieroglyphics", which can also be called "hieroglyphs". Strictly speaking, however, ideograms represent ideas directly rather than words and morphemes, and none of the logographic systems described here are truly ideographic.
Since logograms are visual symbols representing words rather than the sounds or phonemes that make up the word, it is relatively easier to remember or guess the sound of alphabetic written words, while it might be relatively easier to remember or guess the meaning of logograms. Another feature of logograms is that a single logogram may be used by a plurality of languages to represent words with similar meanings. While disparate languages may also use the same or similar alphabets, abjads, abugidas, syllabaries and the like, the degree to which they may share identical representations for words with disparate pronunciations is much more limited.
Logographic systems, or logographies, include the earliest true writing systems; the first historical civilizations of the Near East, China, and Central America used some form of logographic writing.
A purely logographic script would be impractical for most languages, and none is known apart from one devised for the artificial language Toki Pona, a purposefully limited language with only 120 morphemes. All logographic scripts ever used for natural languages rely on the rebus principle to extend a relatively limited set of logograms: A subset of characters is used for their phonetic values, either consonantal or syllabic. The term logosyllabary is used to emphasize the partially phonetic nature of these scripts when the phonetic domain is the syllable. In Chinese, there has been the additional development of fusing such phonetic elements with determinatives; such "radical and phonetic" characters make up the bulk of the script, and Chinese has relegated simple rebuses to the spelling of foreign loan words and words from non-standard dialects.
Logographic writing systems include:
None of these systems was purely logographic. This can be illustrated with Chinese. Not all Chinese characters represent morphemes: some morphemes are composed of more than one character. For example, the Chinese word for spider, 蜘蛛 zhīzhū, was creating by fusing the rebus 知朱 zhīzhū (literally "know cinnabar") with the 'bug' determinative 虫. Neither *蜘 zhī nor *蛛 zhū occur separately (except to stand in for 蜘蛛 in poetry). In Archaic Chinese, one can find the reverse: a single character representing more than one morpheme. An example is Archaic Chinese 王 hjwangs, a combination of a morpheme hjwang meaning king (coincidentally also written 王) and a suffix pronounced s. (The suffix is preserved in the modern falling tone.) In modern Mandarin, bimorphemic syllables are always written with two characters, for example 花儿 huār "flower (diminutive)".
Logograms are used in modern shorthand to represent common words. In addition, the numerals and mathematical symbols used in alphabetic systems are logograms 1 one, 2 two, + plus, = equals, and so on. In English, the ampersand & is used for and and et (such as &c for et cetera), % for percent, $ for dollar, # for number, € for euro, £ for pound, etc.
The first two types are "single-body", meaning that the character was created independently of other Chinese characters. Although the perception of most Westerners is that most characters were derived in single-body fashion, pictograms and ideograms actually take up but a small proportion of Chinese logograms. More productive for the Chinese script were the two "compound" methods, i.e. the character was created from assembling different characters. Despite being called "compounds", these logograms are still single characters, and are written to take up the same amount of space as any other logogram. The final two types are methods in the usage of characters rather than the formation of characters themselves.
The most productive method of Chinese writing, the radical-phonetic, was made possible because the phonetic system of Chinese allowed for generous homonymy, and because in consideration of phonetic similarity tone was generally ignored, as were the medial and final consonants of the characters in consideration, at least according to theory following from reconstructed Old Chinese pronunciation. Note that due to the long period of language evolution, such component "hints" within characters as provided by the radical-phonetic compounds are sometimes useless and may be misleading in modern usage.
Within the context of the Chinese language, Chinese characters by and large represent words and morphemes rather than pure ideas; however, the adoption of Chinese characters by the Japanese and Korean languages (where they are known as kanji and hanja, respectively) have resulted in some complications to this picture.
Many Chinese words, composed of Chinese morphemes, were borrowed into Japanese and Korean together with their character representations; in this case, the morphemes and characters were borrowed together. In other cases, however, characters were borrowed to represent native Japanese and Korean morphemes, on the basis of meaning alone. As a result, a single character can end up representing multiple morphemes of similar meaning but different origins across several languages. Because of this, kanji and hanja are often described as morphographic writing systems.
This separation, however, also has the great disadvantage of requiring the memorization of the logograms when learning to read and write, separately from the pronunciation. Though not an inherent feature of logograms, Japanese has the added complication that almost every logogram has more than one pronunciation. Conversely, a phonetic character set is written precisely as it is spoken, but with the disadvantage that slight pronunciation differences introduce ambiguities. Many alphabetic systems such as those of Greek, Latin, Italian and Finnish make the practical compromise of standardizing how words are written while maintaining a good one-to-one relation between characters and sounds. English orthography is more complicated than that and character combinations are often pronounced in multiple ways. Hangul, the Korean language writing system, is an example of an alphabet that was designed to replace the logogrammic hanja in order to increase literacy. The latter is now rarely used in Korea.
Also due to the number of glyphs, in programming and computing in general, more memory is needed to store each grapheme as the character set is larger. As a comparison, ISO 8859 requires only one byte for each grapheme, while the Basic Multilingual Plane encoded in UTF-8 requires up to three bytes. On the other hand, English words, for example, average on five characters and a space per word and thus need six bytes for every word. Since many logograms contain more than one grapheme, it is not clear which is more memory-efficient. Variable-width encodings allow a unified character encoding standard such as Unicode to use only the bytes necessary to represent a character, reducing the overhead that follows merging large character sets with smaller ones.