Just in case anyone is following this thread without the "benefit"

of a recent education in the humanities, fine arts, or certain social sciences, the following explanations of post-modernism might be helpful:
www.pbs.org/faithandreason/gengloss/postm-body.html
www.georgetown.edu/faculty/irvinem/theory/pomo.html
Actually, if you just google "post-modernism" and check out the .edu sites, you will find professors trying to make it intelligible to their undergraduate students.
In the following paragraphs, I am not sticking up for post-modernism, simply trying to explain it.
As with any kind of intellectual endeavour, there are "lumpers" and "splitters." The lumpers would group theories/schools of thought like post-modernism, post-structuralism, deconstruction, critical studies, post-colonialism, and parts of semiotics into the post-modern camp. The splitters would see them as distinctly separate.
Essentially, and in my limited understanding, the modern condition and what preceded it insisted upon one "right" way of understanding reality. 1000 years ago, clerics believed there was one correct religion, and the others were heresy. Or 50 years ago many secular people believed that science and technology were entirely on the right track, and religion was bunk. Or that English norms were the pinnacle of cultural evolution, and other cultures were inferior. And so on.
In astrological terms, we might think of a modern and pre-modern condition as highly given to orthodoxy. Even if the orthodoxy is permissive and eclectic. (Remember the 70's mantra: "You do your thing, and I do my thing. If we find each other, it's beautiful." Heaven forbid one should profess a different view of personal relationships!)
So traditional astrology was pretty orthodox. I sometimes think this had less to do with its techniques then with its delineation of human character. People simply were a particular way, for good or ill. Personalities were not fluid, indeterminate, and evolving. One's personality didn't depend upon whether one lived in one's birthplace in familiar surroundings, or might live in a foreign country where his traits might be considered unusual. Characters were fixed at birth. Even a good or bad old age followed by the reverse earlier in life was set and pre-determined.
We actually find something comparable in "modern psychological astrology" in which the modernist Freud had clear views about proper gender roles, as translated into statements about the moon (the "bad" mother) in the horoscope.
Orthodoxy before post-modernism manifested itself through observable
discourses, which were the combination of cultural beliefs expressed in narrative form, artefacts, and practices.
In astrological terms, astrologers have all kinds of beliefs about the horoscope and its contents, and they manifest these through chart interpretations to clients, including the way in which the interpretation is delivered (say, via phone, in-person, or e-mail.) We could call these collectively an astrological discourse.
So first, off, post-modernism indicates that all of our beliefs and practices are culturally conditioned, and highly influenced by variables like our historical period, location, ethnicity, socio-economic class, nationality, and gender. There simply is no template or yardstick out there against which the "truth" or "reality" could be measured with the non-orthodox interpretations found less good (
cultural relativism or multi-culturalism.)
Common narratives from modernity are ideas like the unmitigated benefits of "progress" or that science will ultimately have all the answers and bestow upon us the blessings therefrom. Common narratives that span pre-modernity and modernity are ideas about the necessity and benefits of existing political and institutional heirarchies.
Second, the relationship between an astrological or other discourse and reality is fundamentally unknowable, because we can only see things through our own cultural lenses-- or blinkers. Even science is a product of people coming from their own cultural biases. Sciences Studies, another type of post-modernism in the generic sense, has shown how purportedly objective scientific research actually displays significant cultural biases.
Apparently astrologers deal with 30-degree signs and a 360-degree zodiac, in part because Babylonians worked with a base-60 arithmetic system, for example. There isn't anything objective out there in the sky about 360 degrees. There isn't anything objective about a tropical zodiac, which is merely a cultural construct about linking pie-sectors of the heavens to the solar equinoxes and solstices. And it is highly cultural to decide that these dates matter somehow to personal development.
Post-modernism has a following in the arts and architecture. The buildings of Frank Gehry would be an example. Or just imagine a book in which the pages are collated in no discernable order, because the idea that they should be organized sequentially is our unthinking residue from a poorly contemplated cultural practice.
The above is just a hint of a glimpse into an introduction to post-modernism as most people would understand it. At its extreme, everything we thought we know is up for grabs. This view is either scary or liberating, depending upon how entrenched one is in customs and norms.
This is why I think it is unfortunate that Robert Hand used the term post-modernism, because it has had an extensive vigorous intellectual life on its own.
Once we get beyond that, I think he has some good things to say about the revival of traditional astrology.