Speech balloons (also speech bubbles, dialogue balloons or word balloons) are a graphic convention used most commonly in comic books, comic strips and cartoons to allow words (and much less often, pictures) to be understood as representing the speech or thoughts of a given character in the comic. There is often a formal distinction between the balloon that indicates thoughts and the one that indicates words spoken aloud: the bubble that conveys subjective thoughts is often referred to as a thought balloon.
In Western graphic art, labels that reveal what a pictured figure is saying have appeared since at least the 13th century. Word balloons began appearing in 18th century printed broadsides and political cartoons from the American Revolution often used them. http://www.nhc.rtp.nc.us/tserve/eighteen/ekeyinfo/erelrev.htmhttp://xroads.virginia.edu/~MA04/wood/ykid/illustrated.htm With the development of the comics industry in the 20th century, the appearance of speech balloons has become increasingly standardized, though the formal conventions that have evolved in different cultures (USA as opposed to Japan, for example), can be quite distinct.
The Yellow Kid is generally credited as the first American comic strip character. His words initially appeared on his yellow shirt but word balloons very much like those in use today were added almost immediately, as early as 1896. By the start of the 20th century the use of word balloons was ubiquitous, and since that time only a very few comic strips and comic books have relied on captions, notably Hal Foster's Prince Valiant and the early Tarzan comic strip. For many years, word balloons were less common in Europe than in the USA, or were used together with captions. One example is the Dutch cartoonist Marten Toonder's comics about Tom Puss and Oliver B. Bumble, where the literary captions are printed out below the strip and almost take up as much space as the drawings, so that the strip fills twice the space of most newspaper strips. A similar example from the UK is Rupert Bear.
The most common is the speech bubble. It comes in two forms for two circumstances: An in-panel character and an off-panel character. An in-panel character (one who is fully or mostly visible in the panel of the strip of comic that the reader is viewing) uses a bubble with a pointer, called a tail, directed towards the speaker.
When one character has multiple balloons within a panel, often only the balloon nearest to the speaker's head has a tail, and the others are connected to it in sequence by narrow bands. This style is often used in Mad Magazine, due to its "call-and-response" dialogue-based humor.
An off-panel character (the comic book equivalent of being "off screen") has several options, some of them rather unconventional. The first is a standard speech bubble with a tail pointing toward the speaker's position. The second option, which originated in manga, has the tail pointing into the bubble, instead of out. (This tail is still pointing towards the speaker.) The third option replaces the tail with a sort of bottleneck that connects with the side of the panel. It can be seen in the works of graphic novelist Marjane Satrapi (author of Persepolis).
In American comics, a bubble without a tail means that the speaker is not merely outside the reader's field of view but invisible to the viewpoint character, often as an unspecified member of a crowd.
Characters distant (in space or time) from the scene of the panel can still speak, in squared bubbles without a tail; this usage, equivalent to voice-over in film, is not uncommon in American comics for dramatic contrast. In contrast to captions, the corners of such balloons never coincide with those of the panel; for further distinction they often have a double outline, a different background color, or quotation marks.
Thought bubbles come in two forms: the chain thought bubble and the "fuzzy" bubble.
The chain thought bubble is the almost universal symbol for thinking in cartoons. It consists of a large, cloud-like bubble containing the text of the thought, which is connected to the area next to a character by a chain of increasingly smaller circular bubbles.
In manga, the method of depicting thought is different. Instead of a cloud, the thought is encircled in a shiny halo.
Another, less conventional thought bubble has emerged: the "fuzzy" thought bubble. Used in manga (by such artists as Ken Akamatsu), the fuzzy bubble is roughly circular in shape (generally), but the edge of the bubble is not a line but a collection of spikes close to each other, creating the impression of fuzziness. Fuzzy thought bubbles do not use tails, and are placed in the area of the character who is thinking. This has the advantage of reflecting the TV equivalent effect: something said with an echo.
Writers and artists can refuse to use thought bubbles, expressing the action through spoken dialogue and drawing; they are sometimes seen as an inefficient method of expressing thought because they are attached directly to the head of the thinker, unlike methods such as caption boxes, which can be used both as an expression of thought and narration while existing in an entirely different panel from the character thinking. However, they are restricted to the current viewpoint character. An example is Alan Moore and David Lloyd's V for Vendetta, wherein during one chapter, a monologue expressed in captions serves not only to express the thoughts of a character but also the mood, status and actions of three others.
In modern British and American adventure comics, the thought balloon is often replaced by an inner monologue in captions, as described above.