Astrology is an intuitive art. It's not Science, although it's based on scientific knowledge, as all art is. But it does not replace, supplant, or go against science in any way. Rather, it picks up where science leaves off. It goes beyond what our logical mind knows, beyond what data can tell us, into the realm of what we can only know in our bodies, in our guts, in our subconscious mind. It accesses information we can only understand through metaphor, mythology, and imagination. The Western Tropical Zodiac is a system that was first developed by the ancient Babylonians and then perfected in ancient Greece and Rome. In my practice, I use a blend of the classical and modern approaches. I prefer the ancient system of planetary rulership over the modern system, but I do use a modern house system (Placidus.) The ancient rulership system was set up very elegantly - The Sun and Moon, as the biggest, brightest lights in our sky, each ruled one sign and all of the other planets that were visible to the naked eye (Mercury - Saturn) each ruled two signs. "Rulership," was called "domicile," which meant that a planet was "at home" in that sign. It meant it was comfortable: it could do whatever it wanted without interference; it was "in charge" of those signs and any planets in them.     When the modern planets were discovered, astrologers felt that these needed to be worked into the ancient system of rulership, and so they were assigned to zodiac signs that they shared certain qualities and similarities with. So, Aquarius was taken away from Saturn and given to Uranus; Scorpio was taken away from Mars and given to Pluto; and Pisces was taken away from Jupiter and given to Neptune. However, these new assignments were not based on how well or strongly a planet functioned in a particular sign, but on how similar it was to that sign. This, essentially, screwed up the existing system.     The ancient system was based on thousands of years of observation. The ancient Babylonians, Greeks, and Romans were people who had no electricity, no electric lights, no TV, no internet. They had little else to do at night other than keep a close watch on the movements of the millions of tiny lights in the sky. They thought about their study of the night sky as "reading" the sky for messages and omens, the idea being that the patterns these lights in the sky followed mirrored the patterns of human life on Earth. So, they personified the planets and made up stories about them. They tracked the patterns of their movements and correlated them to human experiences. And sure, they couldn't see all of the lights that were up there, as some were just too far away. But there was nothing that was missing from their interpretations. The ancient system did a fine job of relating the movements of the planets to human experience.     The way I think of the outer or "modern" planets is that they do not "rule" any signs. They share similarities with some, sure, but they are are not "in charge" of any. They are so far away from us that they cannot be seen without special equipment, and they move so slowly through our sky that they have less to tell us about our own personal lives and more to tell us about our generation and the eras of history we live through. They each take anywhere from 7 to almost 20 years (Pluto) to travel through one zodiac sign, so everyone born during that time will have that planet in the same sign. If you have an outer planet that makes a significant aspect (by natal aspect or transit) to an inner planet (or a "personal"/ "interpersonal" planet) in your chart, then it may have more to tell you about yourself personally, but usually, we don't know what messages an outer planet has for us until we're old enough to look back on decades of our lives.  I use a modern house system, though, because I personally feel it's more accurate. Ancient people did not have the technology to measure the sky with the precision that we can today, and in fact, the zodiac signs were developed simply as a way to measure the sky by dividing it up into twelve 30 degree slices. The houses, which essentially measure the space between us and the sky, were aligned with the signs, with each 30 degree sign occupying a 30 degree house. This system is called the "Whole Sign" house system. There are a number of different house systems and there is heated debate among astrologers about them. People get very emotionally invested in the house system they use. However, what I believe is that there is no "right" or "wrong" house system; there is only what works for you and what doesn't. For me, the whole sign house system does not work because it does not set the ascendant (the point in the sky that was just rising above the horizon at your time of birth) as the actual horizon. Instead it buries it down inside either the first or even second house. Placidus houses, however, use your rising degree as the cusp of the first house, setting it at the actual "horizon line" of the chart. I find this to be much more accurate particularly for people who have a late degree of a sign rising (15- 29 degrees.) If you have an early degree rising, then whole sign houses probably work fine for you. Also, I don't believe in sign "cusps." Far too much emphasis is placed on the signs in most pop-culture spaces. The signs are not the most important thing in your chart. The planets are. If you think of your chart as a movie set, the planets are like the actors; the signs are the parts they play - their costumes, hair and make-up, the dialect they use, etc.; and the houses are like the different locations on the set. Barring modern special effects, an actor cannot play two roles at once; cannot wear two costumes at once; and cannot speak in two dialects at once. And a planet cannot be in two signs at once, which is basically what saying it's on a "cusp" is proposing. The most important thing is the actor who is playing the role. The role, itself, is just the vehicle for the actor's expression, or the style in which the actor expresses him or herself. Sometimes, this is a match made in heaven and the actor is playing a role he or she was born to play (i.e. a planet in the sign it rules.) Other times, the actor is totally miscast and does, at best, a clumsy job of portraying that role (i.e.- a planet that's in the sign of its "fall.") The houses are the settings where the action of the metaphorical film takes place. And I do kind of believe in cusps for houses, though, kind of. It depends on the specific situation. But that gets complicated. An actor can't really be in two settings at once, either, but they can occupy a passageway from one location to the next. Depending on the situation, of course. The movie set analogy, which I owe entirely to the great astrologer, Kevin Burke, does start to break down after a bit and is not an exact correlation, but I hope it helps to make things a bit more concrete. In your actual chart, the planets represent basic drives and aspects of your personality, the signs represent the style in which you express those drives and personality traits, and the houses represent the areas of life where these basic elements of your personality are likely to show up. However, it's important to remember that astrology is just a system that facilitates our understanding of ourselves. In reality, there are no separate, discrete drives or traits or "areas" of our lives. It's all us, and it's all our lives. Breaking a person's life and personality down into these separate elements helps us understand what's going on, but ultimately, we have to look at a chart, ourselves, and our lives, as one whole thing.