Apologies in advance in case this comes across as a bit blunt:
There seem to be some unusual definitions of "a tight grab" as well what constitutes "a relaxed grab" as well as the power of such a grab. A tight grab doesn't need reams of explanation. If you ask me to grab you tightly, I'll try to grab you tightly.
Perhaps this sounds too simple, but imagine your opponent is going to follow up the grab with a punch or other attack with any of their unoccupied limbs. Alternatively, imagine you have multiple opponents and your attacker is one of many attempting to stop you moving so they can all lay into you. In the role of the attacker, is your grab the kind of grab that would succeed in securing that arm, stopping their movement or dragging someone into an alleyway? Can you do any of the above with a light grab and if so, is that basic?
The founder was well known for letting people (often high-ranking martial artists) grab tightly (Tenryu
for example) and many of his direct students do likewise as a method of kokyu
development. Whether other people use this kind of training is up to them. What I don't get is some of the illogical statements people are making to invalidate this practice and elevate their own.
A uke that holds with relaxation, with their centre in their hand/s, full intent on the objective and a completley free to move body, is a completely different animal than the 'tight grabber'. find one of those to test yourself against, they are very easy to move if the principles of aikido are followed and almost impossible to throw if they are not.
Mark, is your definition of grabbing lightly the same as my definition of grabbing tightly? The tight grabs I described above can be done very strongly by weak old masters using aiki alone – but it is still a tight grab, particularly when you give them something to work with by trying to muscle out of it. If this is not your meaning, I guess what confuses me about this post is that I find the opposite scenario: people grabbing tightly with the purpose of immobilising (by muscle or aiki-magic) make it a lot harder to move whereas people grabbing lightly (even if ironically to maintain their freedom of movement – which I also don’t get btw) are usually easy to move even with just a little regular muscle. I understand that in certain ki-forms, there are exercises involving this kind of thing but I think this is a different kind of practice to the basics the OP was talking about. If your opponent is "relaxed" as in only lightly attacking, they can't strike so easily because their physical (and “intentional”) connection isn't strong enough to stop you moving somewhere safer and they can't stop you striking them for the same reason: the attacker only has a tenuous connection that can be broken easily. Usually, the worst the attacker can do is to give up and flee if you mistakenly try to apply a waza to an attack that poses little danger.
It seems to me that if you're going to do a technique on someone who only has a light grab, it has to be this scenario: a fully committed attack in which the opponent is intending to get a solid immobilising grab but you only allow
the light grab.
Also I'm not sure what is meant by "centre in their hands." The most basic, easy-to-explain kind of centre is the centre of gravity.
Kind regards to all