In the Bartimaeus series, spirits (or demons) are otherworldly entities who are made of "essence", don't have real bodies as such, and are able to take on many different forms. Bartimaeus, for example, takes on both male and female human forms over the course of The Amulet of Samarkand, and remarks in a footnote at the start of chapter 4:
For those who are wondering, I have no difficulty in becoming a woman. Nor for that matter a man. In some ways I suppose women are trickier, but I won't go into that now. Woman, man, mole, maggot - they're all the same, when all's said and done, except for slight variations in cognitive ability.
From this one might be tempted to deduce that spirits have no sex or gender. But Bartimaeus, of course, is consistently referred to as "he"; his friend Queezle is always "she"; and other spirits are also given gendered pronouns (at least from Bartimaeus's point of view; humans often use "it" for demons, but that's just, well, dehumanising). Even for spirits that he hasn't met before, Bartimaeus seems able to know at a glance whether to refer to them as "he" or "she".
What does gender mean for spirits, then? Is it related to some physical characteristic of their essence (rather than the forms they choose to take in our world)? Does it reflect some aspects of their personalities? Does it relate to the type of forms they generally take in our world (most of Bartimaeus's forms are male, and he notes Queezle's form as a she-leopard specifically)? Is it just a personal choice?
