YUAN, eminent, means (literally) a person’s head.
Meanings: first, chief, great, primary, fundamental, good, spring. The Yuan-sacrifice is a sacrifice brought in spring, in the time of the beginning of growth, the time of sowing. When it says in a hexagram ‘yuan’, this means there is an opening, new fields for things to happen or make them happen, new paths. There is creative potential, or material to work with. Resources are still small, but do with them whatever you can. Make the best use of them, and don't be afraid to invest them.
HENG, expansion, is also the name of a sacrifice, one brought in summer. The crop is growing, and now the gods are implored to make it a big and rich one. There are already enough proceeds to offer to them, so this sacrifice is two-way: offering and receiving. In a hexagram it indicates expansion, growth, success, abundance. If you're willing to offer from what you have, it will make your profits larger. Stingy people rarely make a success of anything. Important too is to believe in what you do. Confidence is a great fertilizer. Indicates success, things going smoothly.
ZHEN, determination or divination, is oracle-consulting, but also receiving an answer. And most important: to follow the advice of the gods. That is why it is usually translated as perseverance, determination, correctness, loyalty, chastity. Everyone has a different name for the gods: God or intuition or Manitou or the spirit of grandmother. It is not really important, what counts is if one listens. So when it says ‘determination auspicious’ it is good in this context to ask your higher counselor what to do, and to stick to it. Sometimes, not very often, it says determination is not favorable. Then one should be open and alert and react to every new moment. Without any predetermined course. Not even with too much virtue. Virtue is a good thing, but in some circumstances a little less virtue can save one from calamities. The Yi is practical: it wants the highest spirit possible, but not your misfortune.
(more about zhen on page 'Divination and repentance')
About yuan, heng, li and zhen:
According to the records of Zuo zhuan xiang gong jiu nian 左传·襄公九年 (the Ninth Year during the Reign of Duke Xiang of State Lu) (i.e., 564 B.C.), Mu Jiang 穆姜, the princess of State Lu, died in the East Palace. Before her being imprisoned into this palace due to the variety of her faults, she had conducted a divination, encountering with hexagram Gen ( , 52) to ba ( 八, lit., eight):
The official diviner interpreted: “It is called Gen to Sui ( , 17). Sui (indicates) following out. (This indicates) you will soon be released.”
Jiang responded: “It states in the Zhouyi : ‘ Sui 随 (following), yuan heng li zhen 元亨利贞 (lit., Sui indicates penetrating, advantageous, correcting and firm even in the very beginning), there will be no error.' (As the saying goes,) yuan connotes the head of the body, heng the assemblage of excellences, li the harmony of all that is right, zhen the faculty of action. Those embodying benevolence are fit to preside over man; he who presents the assemblage of virtues is fit to show in himself the union of all propriety; he who benefits all creatures is fit to exhibit the harmony of all that is right; correct and firm, he is fit to manage (all) affairs. If all these qualities have been correctly accomplished, there will be no error in following. Now for me, as a woman, I committed incest. Therefore, that I who is in low position and conduct no benevolence could not match (the quality of) yuan ; my not being loyal to the state is incongruous with (the quality of) heng; my abdication from the venerable position and coquettishness can not be called zhen. Those who possess the four virtues (of yuan, heng, li and zhen ) can follow out without any error. Now, none of them is in the possession of me, how can I follow out? On the contrary, as I have conducted much malevolence, can I have no error? So, I will certainly be sentenced to life in here and will never be released.”