Okay, first off I will lay out one broad assumption: that the inner chapters of the Chuang-tzu are, by and large, representative of a single author - whom I am happy to call 'Chuang-tzu'. I think we have pretty good reasons to assume this but I won't detail why for the sake of space. For ease I will refer to the text of inner chapters of the Chuang-tzu by using the italicized form Chuang-tzu.
It seems to me that there is something idiosyncratic about this author, he has concerns and themes that we don't find elsewhere in Chinese thought of the Warring States period and certainly not in the Lao-tzu. These themes are almost too varied to draw up a complete list but here are five of the dominant ideas which are characteristic of the Chuang-tzu. I will re-iterate this again at the end but none of these themes are found anywhere in the Lao-tzu:
1 Focus on yu 遊 - wandering/roaming:
This character appears in the Chaung-tzu almost as frequently as the character Tao (at least 30 times by my count). There are a couple - but only a couple - of instances when it is used in the 'normal' sense of to wander about physically. However the vast majority of uses have broader importance. In particularly the theme of 'wandering beyond/outside of' normal ways of thinking, here are two examples:
...he rides the vapour of the clouds, yokes flying dragons to his chariot, and raoms beyond the four seas... - Ch 1 (this phrase 'roaming beyond the four seas' is repeated in Ch 2.)
"They are the sort that roam beyond the guidelines," said Confucius, "I am the sort that roams within the guidelines." - Ch 6
By my count there are as many as 10 uses of 'roams beyond/outside of'. The use of roaming is also, on at least three occasions, explicitly linked to the process of thinking - using the 'heart' (hsin 心). eg "...let the heart roam with other things..." - Ch 4.
It is also linked to the activity of sages: "where-ever the sage roams..." - Ch 5; [Hsu Yu said] "how are you going to roam that free and easy take-any-turn-you -please path?" - Ch 6 ;"Become wholly identified with the limitless and roam where there is no foreboding of anything" - Ch 7.
2 Use of specific examples from nature:
The Chuang-tzu makes repeated use of natural examples to back up his points everything. From "fish forgetting each other in the lakes" (a phrase actually repeated in the Old Tan / Confucius dialogues) to the extraordinary speech of Wang Ni in Ch2, the whole of the Chuang-tzu is replete with examples drawn from nature. There are so many examples of this that I will not waste time quoting them. However what is particularly noticeable is that on the two occasions in the Chuang-tzu we are given direct 'quotes' from the man himself he makes use of such natural examples:
In conversation with Hui tzu he says "Haven't you ever seen a wild cat or weasel? It lurks crouching low ... But the Yak now, which is a big as a cloud hanging from the sky ..." - Ch 1.
Similarly in many of the stories about the man Chuang-tzu from the outer + miscellaneous chapters we find this theme again and again - see, for example, the story of Chuang-tzu hunting Ch 20, his rejection of office Ch 32 (also quoted Ch 63 Shih-chi), his attempt to borrow grain from the Marquis of of Chien-ho Ch 26, his discussion on uselessness with disciples Ch 20 etc... It seems that those writing about the man Chuang-tzu remembered his use of examples drawn from nature almost more than any other aspect of his teaching (and it is notable that given the commonality of this motif in the above stories how divergent some of their philosophy is, take for example the Yangist overtones of the hunting passage vs the Synchretist flavour of his discussion with disciples.)
3 The use of uslessness:
Of all of these main themes this is the one which seems wholly unique to the Chuang-tzu, as far as I am aware, no other Chinese thinker advocates for the useless as Chuang-tzu does. In fact in the Lao-tzu 'useful' is always used in a positive sense, (eg - "emptiness acquires use") exactly the opposite of the position we find in the Chuang-tzu!
The most memorable and detailed of the 'use of the useless' narratives are found in the mid-section of Ch 4 (the 'useless' trees) and Ch 5 (the 'useless' cripples); however the theme crops up in other places as well - the discussions between Chuang-tzu and Hui-tzu in Ch 1; a fragment of a cripple story in Ch 3 (probably dislocated from the Ch 5 series); the closing lines of Ch 4: "All men know the uses of the useful but no one knows the uses of the useless."
4 Particular criticism of Confucius' historical strategy as flawed:
This particular criticism of Confucius is not found in the Lao-tzu. However in the Chuang-tzu it is mentioned on a couple of occasions; most explicitly in the 'Madman' of Chu's speech to Confucius at the end of Ch 4: "Of the age to come we can't be sure // To the age gone by we can't go back" (interestingly in the same speech Confucius is accused of 'interfering with the madman's 'roaming': "Thistle, thistle, // Don't wound me as I walk. // My walk goes backward and goes crooked, // don't wound my feet.")
We also find this theme implicit in Confucius' own realization that he cannot 'roam outside the rules' and his identification as a man 'manacled by heaven' by Old Tan both in Ch 6.
5 Subversion of Confucian characters into Taoist heros:
As is often pointed out the Lao-tzu has a strange characteristic of not mentioning characters at all. In the Chuang-tzu we are met by a whole motley crowd. What is particularly interesting is that so many of them are taken from Confucian literature. For example the above mentioned 'madman of Chu' (Chieh Yu) appears three times in the Chuang-tzu and is taken from Ch 18 of the Analects. We also have Ch’u Po-yu the wise man of Wey, Yen Hui, Old Tan, and, of course Confucius himself, all originally Confucian characters and all, at various points of the Chuang-tzu, acting as Taoist spokespeople.
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There are two reasons I have selected these five themes from the Chuang-tzu: firstly they represent five majour themes by which I think we can identify the voice of the Chuang-tzu's author. Secondly they are all themes absent from the Lao-tzu.
If we read the seven passages from Ch's 12, 13, 14 (x3) and 21 which detail the meeting of Old Tan and Confucius we find all of these themes articulated clearly in Old Tan's dialogue. I am willing to provide detailed examples but I'm sure you have a copy of the Chaung-tzu lying around and can look for yourself ; plus this post has gone on far too long and my wife is getting that look in her eye that tells me my time is almost up...
On the other hand we get none of the language of the Lao-tzu (ie 'root', 'mother', 'unknowable', 'valley', 'emptiness', 'wu' (other than one single use of wu-wei) etc...).
Thus it seems plausible that the author(s) of these fictional meetings of Old Tan and Confucius based the character of Old Tan on the philosophy found in the Chuang-tzu rather than the Lao-tzu. It seems to me that it is Chuang-tzu's voice we hear coming from Old Tan's lips.
