Isn't funny how in the martial arts, as in life, the simplest questions are always the most difficult to answer? There's probably a lesson to be learned there.
A complete answer to your question would probably take weeks to communicate, so I hope it will suffice for me to lay the groundwork for you to find out on your own.
Tae Kwon Do is a Korean martial art which emphasizes kicking techniques, and a tactical preference to maintaining distance (to facilitate the superiority of the kicking techniques). Stylistically, it is an amalgam of methods from other (foreign) styles which were modified to fit the existing Korean style of Taek Kyon (this is also the synthesis of several other Korean styles).
The term 'Kung Fu', is a term which is broadly-encompassing. The multitude of varities of Kung Fu simply defy categorization. The simplest answer, would be that Kung Fu (alternatively, Gung Fu), is a term which is used to describe (possibly) several hundred methods of Chinese unarmed and armed combat.
Jujutsu is, today, a reference to Japanese methods of grappling and groundfighting, with additions and alterations made to suit individual styles and methods. At one point, the term "jujutsu" was used much like the modern English term "unarmed combat"- it referred to no particular style or method, but simply referred to the general topic of hand-to-hand combat. There are essentially three distinctions of jujutsu- sengoku, which are almost totally grappling and groundfighting oriented; edo, which often include striking and kicking techniques (and often, other skills which may not be directly related to combat skills); and aiki, which I will address later.
Judo is, simply, a simplification of many styles of jujutsu, with particularly injurious techniques removed, for application as a sport, and was founded by Jigoro Kano. To understand the greater significance of this transformation, one would require a better understanding of the period of time in which Judo was founded, than I can lay out in one paragraph.
Lastly, Aikido (my own style). Aikido began as an outgrowth of the aiki principle, as taught in the aiki schools of jujutsu (see above). The aiki principle, simply stated, is the blending of one's self with an opponent(s). The more simplistic, and more trite, way of saying this is "Use his own force against him", which is suitable for use as a basic explanation but is somewhat flawed as a complete explanation. Stylistically, aikido is extrapolated from an amalgamation of aiki jujutsu (particularly, Daito Ryu Aiki Jujutsu) techniques and unconstructed Iaido (swordsmanship) footwork and movements. This original amalgamation was called "aiki budo", and the later extrapolation called "aikido". Both were conceived by Ueshiba Morihei, who is known to aikidoka as "O'sensei", or "The Great Teacher".
This should be sufficient to allow you to begin reading and, hopefully, training.
Undoubtedly, there will be some dissention to this summary- after all, this topic is so large and complex, that confusion in inevitable.
Last edited by Roundeyesamurai; 07-22-2005 at 23:02..