Sorry, it’s a history lesson!!!
Actually, there is a great deal of variety in aikido. There is precious little standardization.
I would divide aiki into four main forms.
The first, and oldest is aikijutsu, the oldest school of which I know is Daito-ryu, which dates back to the 12th century, and is arguably one of the only truly indigenous Japanese martial arts (together with kenjutsu/do, and sumai). Most jujutsu is said to come from this style. It is still practised in Kanto and a couple of other places, but is not too common. I have heard of a school in the north of the UK but there is no mention of it on the Daito-ryu main site. The hombu is in east Tokyo, and they don’t really take too kindly to MA hobbyists, by which they mean people who are only wanting to do it for a few years! From what I’ve seen, it is a very solid style, looking like main styles of jujutsu, with aiki principles (more later!).
The three other main modern aiki styles come through Ueshiba Morihei (the Yip Man of aiki). He learned Daito-ryu to the highest level, also Yagyu-ryu kenjutsu, jukenjutsu (?) - a bayonet form, yarijutsu (straight spear), jojutsu (maybe 4’ stick) and maybe a couple of other things. He proved himself in the Japanese military many times (he was stationed in Mongolia, allegedly in a special forces detail, so nobody knows exactly what he did). He formed aiki as we know it in 1924, I think. THE western (maybe world) authority on Ueshiba is an author and aikidoka called John Stevens.
Ueshiba’s original aiki was hard, fast and not at all flowery. Very very effective. Yoshinkan Aikido (anyone read ‘Angry White Pajamas’? - about the Japanese riot police course? 
)is one modern example of this kind, though is a little more angular, I think, than U’s original stuff.
Later in his life Ueshiba got a little (how do I put this without disrespect?!) freaky :rolleyes: . He saw three visions, telling him to abandon violence and to use aiki to promote world peace. Modern Ki-aikido (from a branch ‘founded’ by Tohei Koichi) is an example of aiki from the ‘freaky’ period! As the name suggests (ki in Japanese is chi in Chinese: internal energy, spirit, steam, breath however you care to translate it) it is very internal. This takes perhaps the longest to learn. I’ve trained with ki-aikidoka who I would describe as flowery, balletic, and as wet as a haddock in a bathing costume :o! I’ve also trained with ki-aikidoka who can throw you like a doll, and definitely have whatever ‘IT’ is in the internal CMA 
. There seems to be a lot of skipping in some forms of ki-aiki 
. Bad idea ! A lot of the ‘ki-training’ seems like a watered down tai-chi, and the technique is ineffective to say the least. The good stuff seems good however.
The last common ‘style’ is ‘Ueshiba style’. This group covers a multitude of sins :rolleyes: … the full range from the hippy**** nonsense of the wettest ki-aikidoka, to the hardest, fastest, meanest, baddest assed jujutsu-type grabbit-wrenchit-lockit-breakit stylists!
All aiki is based on principles familiar to many CMA, internal and external: eg, the use of the attackers’ energy against him; circular evasion and deflection to ‘flow’ through the centreline (and centre of balance); triangular entry techniques (using a t-stance, speed, and sharp strikes to nerve points) etc. You can see many katana techniques and spear techniques in there, and weapons (bo - 4.5-6’ staff, and bokuto/bokken - wooden katana especially) are trained extensively in many styles. Some say that the internal aspect is very much based on an extension of energy from the tanden through te-gatana - handblade (with optional imaginary weapon!), so most of it is open hand. Various styles use more or less ki-training, weapons work, realistic attacks, atemi - strikes, etc.
The vast majority of aiki nowadays has some element of said hippy philosophy, but at its root, are we all not training to avoid having to kill someone;)?
Chiba Kazuo (if it is he?) was definitely a renowned g-w-l-b-it stylist in his day. He learned direct from Ueshiba, in the middle period. Now I’ve heard he has mellowed. I hear he is very traditional, and uses bokuto to illustrate his techniques, and ‘extension’. He is one of the only aikidoka I would REALLY REALLY love to train with. Dunno anything about his juniors.
After all that, I know diddly-squat about san-shou yet. Sorry.
