tao teh ching 14

Look, it cannot be seen - it is beyond form.
Listen, it cannot be heard - it is beyond sound.
Grasp, it cannot be held - its is intangible.
These three are indefinable;
Therefore they are joined in one.

From above it is not bright;
From below it is not dark:
An unbroken thread beyond description.
It returns to nothingness.
The form of the formless,
The image of the imageless,
It is called indefinable and beyond imagination.

Stand before it and there is no beginning.
Follow it and there is no end.
Stay with the ancient Tao,
Move with the present.

Knowing the ancient beginning is the essence of Tao.

The Ma wang tui text is markedly different, so I give it in full here:

We look at it but do not see it;
We name this 'the minute'.
We listen to it but do not hear it;
We name this 'the rarified'.
We touch it but do not hold it;
We name this 'the level and smooth'.

These three cannot be examined to the limit.
Thus they merge together as one.
'One' - there is nothing more encompassing above it
And nothing smaller below it.
Boundless, formless! It cannot be named
And returns to the state of no-thing.

This is called the formless form,
The substanceless image.
This is called the subtle and indistinct.
Follow it and you won't see its back;
Greet it and you won't see its head.
Hold onto the Way of the present
To manage the things of the present
And to know the ancient beginning.
This is called the beginning of the thread of the Way.

Importantly, as Henricks points out, 'the One' (i-che), which is missing in all later texts, is singled out for attention in line 9 and this line and the next in this version thus seem to say that this intangibility - this inconceivability and ineffability - is BOTH the all-encompassing nature of all-and-everything and its terminus post quem... which is to say in the ever-present 'now'.
Also, the standard Lao-tze text has 'Hold onto the way of the past' in line 18 (*). Here, what is being said is that - in this present instant - both the management of what is going on around one and knowledge of the ancient beginning are laid bare...
The idea that the roots of the past contain the seeds of the present is found also in the I Ching, in the Discussion on the Trigrams, and is - of course - an extremely sound idea. However, the idea expressed here is VERY closely related to the Buddhist notion of karma... If you want to know what you have done and believed, look at the quality of your life now - where you live, what opportunities are open to you, the quality of your life and your present set of beliefs. By the same token, if you wish to modify any of these, now is the only moment to change your way of acting and believing.
I've mentioned Whitehead's 'experientially initiated potentialities for experience' before: what you see is what *you* believe to be real because that is how you have come to believe reality to be.
The gorblimey example of this is those who have come through the Nazi deathcamps filled with a burning hatred and a desire fore revenge, those who simply want that period forgotten and be over and done with and get back to their 'ordinary' lives, and those for whom the experiences there have opened them up to varying degrees of compassion, love and understanding... Same 'reality'; different vision...

I'm also interested in the lack of conditional in the first clause of the Ma wang tui version. All other versions seem to say, as does Feng, 'Look - it cannot be seen'. The Ma wang tui, however, seems to say 'of course you see it - you just don't know what you're looking at'.
Also the lines about its having neither back nor front... The I Ching ends with the hexagrams After Completion and Before Completion, and I have always taken this (borne out, I think by the lines of both) to mean that, ordinarily, our attention-span is rather limited and tends to lose interest before things have properly dissolved and be too distracted to notice how they actually begin. The fact is, they begin and end in no-where - the Buddhist will tell you they also have their apparent being there too, but let's ignore that for the moment... Things arise out of and dissolve back into no-thing. If one doesn't actually follow them there, one never comes to really know this.

Wang's commentary (which I always select from, by the way - there's much of his interpretation I don't agree with)(I also find Linn's translation humourless in the extreme) says: It is shapeless, leaving no image, and soundless, leaving no reverberation. Thus it can permeate absolutely everything and reach absolutely everywhere. We cannot get to know it and even less know how to give it a name derived from how it looks, sounds or feels... One might wish to claim that it does not exist, but everything achieves existence because of it; and one may wish to affirm that it does exist, but we do not see a form.This is why the text refers to it as 'the shape of that which has no shape, the image of that which has no existence'...That which is free from form and nameless is the progenitor of the myriad things... remote antiquity may be far from us, but the Tao of then still exists now...

Cheng's commentary emphasises the unity of the three qualities of yi, hsi and wei. He explains:

Yi is 'to level, to eliminate' as if one were looking at a mountain but seeing a plain (*). Hsi means 'small'. Wei means 'obscure, wonderful'... What does 'the three qualities cannot be understood no matter how much you ask about them' mean?As chapter 41 says 'A great sound comes from a small noise. A great form has no shape Tao is hidden and nameless...' and thus unfathomable. 'Yet, when intermingled they form a unity', therefore the Sage makes this unity his touchstone or structure for understanding the world... 'Not bright... not dark' is to say 'yet, when intermingled they form a unity'. Formless and imageless, whetehr one wants to confront or follow it, it always remains unclear. In chapter 21 it says, 'Evanescent and elusive it is, yet there is a form contained within it. Yes, elusive and evanescent, yet there is a substance to it'.

(*) Cf., the image in the I Ching, hexagram 15, Ch'ien, Modesty.

He also reads the remaining phrases as referring to the union of these three qualities, equality and levelness, smallness and obscurity.