I recently attended an astrology lecture, and during the discussion, several audience members seemed to insist that a planet in an example chart with no Essential Dignity was actually well disposed because it happened to be in the First House, which is an Accidental Dignity. The question of which dignities are more important comes up quite a lot, and the short answer is that Essential Dignities are always primary. When you have a planet with no Essential Dignity (or with Essential Debility) that has Accidental Dignity, what you have is lipstick on a pig.
Essential Dignities are, well, essential. They're a fundamental part of the planet itself. They’re based on the specific degree of the zodiac (and the sect of the chart), and they set the context for how that particular planet will express in that chart. Accidental Dignities, as you can tell from the term, have nothing to do with the planet itself, and are circumstantial. A planet in an angular house, for example, is accidentally dignified; so is a planet in good aspect to Jupiter.
As in all things astrological, context is king. First of all, I need to make the disclaimer that the only time you would care about the actual “condition” of a planet in terms of its Essential or Accidental Dignity is if you’re looking at a horary or electional chart. When interpreting a natal chart, the traditional approach to evaluating a planet’s dignity has no practical value. (What matters in natal interpretations are the planets that have dignity for a particular degree — the “Board of Directors” for the planet in question.)
In the context of a horary or electional chart, the Essential Dignity sets the context. If the planet has no Essential Dignity, or is Essentially Debilitated (Detriment, Fall, or Peregrine), that planet will never bring about a good result. Accidental Dignity affects how prominent the planet is in the chart, not how strong it is. Planets in angular houses have easy access to the “doors” that lead to the outside world, so they can be “seen” more clearly, and they get noticed. Planets that aspect Jupiter (classically the “greater benefic”) are made bigger. Bigger is not automatically better, something the classical literature rarely seems to take into account. If you think a peregrine, retrograde Mars in Libra can cause trouble in an electional or horary chart, consider how much damage it could do if it were trine Jupiter and in the 10th house.
A planet that is accidentally debilitated loses prominence, but not strength. Jupiter in Pisces is Essentially Dignified (in Rulership), but if Jupiter in Pisces is in the 3rd house, and combust the Sun (within 8° of the Sun), it’s hidden from view. Planets that are combust the Sun aren't visible at all, and planets in cadent houses are as far away from an angle as you can get. As wonderful as Jupiter in Pisces might be in this chart, it has a very hard time being noticed.
Where Accidental Dignity really begins to matter is when you’re considering a hoary chart where the significators have some Essential Dignity, but not enough to really make a difference (Term or Triplicity). Getting a “yes” answer in a horary chart usually requires not only that the significators be coming together in a harmonious aspect, but also that they each have sufficient strength to overcome any obstacles that may show up along the way. A planet that only has Essential Dignity by Term, but that gains Accidental Dignity might receive that extra boost to increase the chances of a positive result.
Once again, this only applies to horary or electional charts; none of these conditions have any practical value when interpreting a natal chart. If you’d like to learn how to work with Essential Dignities in the context of a natal chart, check out The Real Astrology Academy’s Online Natal Astrology Class.