At the bottom of every animal entry there is a line listing three zodiac signs. It is the thing I am asked about most and the thing I am most careful with, because compatibility is where writing like this most easily tips over into telling people what to do with their lives.
What the three signs actually mean
They mean: people with these signs tend to find this animal's way of operating easy to be around. That is all. It is a note about friction, not a forecast about relationships, and emphatically not advice about who to date.
I have deliberately not built a compatibility calculator and I do not intend to. The moment you drop two people's results into a box and return a percentage, you have made a claim the underlying material cannot support. A line saying this animal sits easily with Aries, Gemini and Scorpio is a conversation starter. A number saying you are 84% compatible is a fabrication with a decimal point in it, and people take numbers far more seriously than they take sentences.
How I decided them
Three inputs, roughly in this order of weight.
The elemental relationships
Traditional astrology holds that signs sharing an element understand each other easily, that fire and air get on, and that earth and water do. Fire needs air; earth holds water. It is an old scheme and a coherent one, and it does most of the work here.
The animal itself
Where the scheme and the creature disagreed, the creature usually won. A Capricorn wolverine is an earth-sign animal by classification, but a wolverine's appetite for fights well above its weight is fire-sign behaviour, and its pairings say so. I chose these animals for how they behave, so it would be strange to then ignore that behaviour when working out who they get on with.
The personality type
The lightest input and the one I trust least. Type theory has plenty to say about which cognitive styles complement each other, but a good deal of it is contested and some of it is folklore wearing a lab coat. I used it to break ties, not to drive decisions.
I did not treat the traditional oppositions as automatic incompatibility. Aries and Libra sit opposite each other on the wheel and a lot of astrological writing reads that as conflict. In practice opposition often describes two halves of one problem, and several pairings here cross the wheel on purpose.
Why there is no incompatible list
I was asked for one early on and thought about it properly before deciding against it. Telling somebody an entire sign is bad for them is the sort of thing people remember, and occasionally act on, and there is nothing underneath it that could justify that weight. The three signs listed are the ones I think sit most easily. A sign's absence from that list means nothing whatsoever.
It is the same reason the descriptions avoid the word should. A description that tells you what you are like is a mirror, and you get to decide whether it fits. A description that tells you what to do is something else, and I am not qualified to write it.
The comparison I find more interesting
Honestly, it is not between people at all. It is between animals.
If your animal is the Gemini ESTJ, go and look at what the other eleven ESTJ animals are: a raven, a jaguar, a stork, an albatross, an emperor scorpion. There is a shape running through those, and it is often clearer than anything your sign alone will tell you. I did not notice it until the grid was finished and I could read it column by column instead of row by row.
The reverse works too. Read all sixteen animals of your own sign and you will see the range a single sign covers, which is the argument this entire project is making. Twelve was never enough.
Both readings start from the Deep Dives index, and neither needs you to take the quiz again.
I research and write the Zodiac & Soul bestiary — all 192 entries, the natural history and the mythology behind each one. More about the project on the About page, or say hello via contact.