A comedian once showed a newspaper to his audience. The headline read, "1-800 Astrology Business Goes Under: They Should Have Seen It Coming." Everyone laughed, including me. We chuckled at the irony of a real contradiction here. If such a business could provide the service they claim, then its owners should have succeeded where other businesses failed. In fact, if they really knew the future, they likely wouldn't bother with this business at all. They would simply raid the stock market with a perfect investing record. We all somewhat instinctively know this, even those of us who have never had the occasion to sit and think it through carefully.
But this pseudo-science has another problem that concerns us. It's adherents who create the garden-variety horoscope columns (found in most any newspaper) spotlight a basic contradiction. On the one hand, they pretend to tell your future based upon the timing of your birth and the alignment of the stars and/ or planets. Philosophers have called this assumption "astral determinism."
This means simply that the stars and planets determine your future, hence the phrase, "written in the stars." On the other hand, however, when the predictors finish telling just what will befall you, they move onto the next part of the column. They offer advice. But this advice you may take or leave, as though you have a free choice to make, the outcome of which no star determines.
So they assume astral determinism when predicting, and then assume its opposite when advising. One simply cannot have it both ways. The only way to resolve this contradiction derives from saying that the heavenlies determine SOME things, but not others. This avoids contradictory impulses, however, at the cost of engaging a purely arbitrary (pick and choose whichever you like) approach to what stars do and do not determine about your life. And yet their charts promise a principled (non-arbitrary) way to know the future. So this option makes no logical headway either.
Either way then, assumptions necessary to the trade of star-traffickers show themselves bogus. The whole thing turns out a useless mirage. Astral determinism thus represents a phoney idea, and we can show this with a little logical rigor.
Finally then, we wish to add logical insult to mystical injury by noting that our refutation of astral determinism posits a fairly clear and obvious problem for their trade. And like the bug who never quite manages to avoid the fast-approaching windshield -- they should have seen it coming.