Jerry—I think part of difference between hsing-i and tai chi may be something of an apples and oranges divide. B.K. Frantzis had some interesting things to say about the differences in martial philosophy and outlook.
"Hsing-i focuses on the direct approach, on being aggressive. Characteristics of the hsing-i mentality include tackling problems head on, overcoming whatever obstacles appear, having an exceptionally strong self-confidence that refuses to accept failure, and a “go for it’ attitude in attaining goals. Mentally, hsing-i practitioners never retreat. They simply view stepping backwards as a temporary tactical situation to allow them to get on with their main business of attack and conquer. The two phrases that characterize hsing-i are: ‘My will be done’ and 'Never retreat.’"
On tai chi: "Tai chi emphasizes softness, attaining goals in an indirect, non-obvious fashion, subtlety, and flowing around obstacles rather than confronting them. Deception, not giving someone a solid place to attack, being subtle and circumspect, and all sorts of counterattack strategies form the core of tai chi's psychological profile. A tai chi orientation will offer minimal or no resistance to an obstacle, person, or situation. Tai chi practitioners yield to an oncoming force, and while appearing to be weak, draw that force into themselves, move around it like water going around a rock, and then counterattack at the most unexpected moment.
The operative phrases in tai chi are: "Forget yourself and follow the other" and, "Thy will be done," so that the opponents get whatever they want, but not in the way they expected it. In the process of giving the opponenet what they want through yielding, tai chi fighters move from a weak position to an advantageous one.'
-excerpted from B.K. Frantzis's book "The Power of Internal Martial Arts: Combat Secrets of Ba Gua, Tai Chi, and Hsing-I" page 77.
So from my own limited personal experience meeting some hsing-i people recently, it seemed like the people I met just didn’t get the tai chi mindset on a gut level, even though they understood the theory. Not that they were bad or wrong, they just had a really different way of looking at the world.
And yet, like all divisions and opposites, there are blending and meeting points--like the long friendship between the hsing-i master Sun Lutang and Yang Chengfu. A couple months ago Yang Jun was concerned that people were getting the wrong impression of Sun Lutang because Yang Chengfu refused to teach him Yang style tai chi, as though maybe YCF didn't want to teach him. This is true, but not for the negative reasons one might suppose. So I’ll share what I remember of the story here. I would just mangle places, names, and dates because I just can’t remember those things at all, so I’ll have to leave them out. I’m very sorry my memory is bad, perhaps someone with a more historical bent can fill in the blanks.
If I remember Yang Jun's story correctly, Sun Lutang originally challenged Yang Chengfu. Sun Lutang was already a hsing-i master and yet in the challenge match neither could win. Later they enjoyed trying each other's skill regularly. The word "try" is important. They weren't "challenging" each other because it was a friendly match. They weren't "sparring" because (to YJ, maybe in Chinese) that means they were training and implies one was teaching the other.
Yang Chengfu was careful to never teach Sun Lutang anything--out of respect for him, not disrespect. The martial code that both respected dictated that one's teacher has to be treated with the respect accorded to one's father's generation. The teacher is like one's father. Because Yang Chengfu respected Sun Lutang and considered him a peer, he didn't want to take the "higher" one-up position of teacher. So they just tried each other’s skill often, and Sun Lutang learned a lot just from experiencing Yang Chengfu’s fighting style. Yang Chengfu introduced Sun Lutang to Hao Wei Chen of the Wu/Hao style so he could pursue his interest in tai chi chuan without it altering their friendship.
In fact they were so respectful of each other that they turned down prestigious positions.
An official invited Yang Chengfu to be the director of a new national martial arts academy. He was busy with this and that and so didn’t respond right away, but he packed up his household and moved to take up his new position. When he arrived, however, he discovered that the official worried that he’d had no response from Yang Chengfu, had invited Sun Lutang to be the new director and Sun Lutang was already there installed in the position!
Sun Lutang’s respect for Yang Chengfu was such that he resigned the directorship. Yang Chengfu’s respect for Sun Lutang was such that he could not accept the directorship in his stead. Both of them left, to the detriment of the fledgling academy. Their friendship was more important than a government position.
The official felt so bad about the whole situation that he commissioned two very expensive high quality swords and delivered them to Yang Chengfu personally.
To this day, the Yang family and the Sun family still have a very good relationship.