# Why does the moment coefficient for angle of attack = 0° not have to be negative?

I know for static stability reasons, the derivative of the moment coefficient of an aircraft has to be negative.

What I do not understand, why the moment of coefficient (cm) at all is allowed to be positive? Because when it is positive the aircraft pitches up.

Is it because when cm>0 I use my tails for trimming ? But is this "static stability" when I actively use my tail ?

I struggle with:
alpha = 0 ° --> e.g. cm=0.3 : the tail is used for trimming so that it counteracts the positive moment of the wing

alpha = 2° -- > e.g. cm=0.4 : now the pilot could also use the tail for trimming the higher moment

An airplane achieves steady flight at a given airspeed only if the total pitching moment about its CG is zero. This is achieved with a particular fixed tail angle/elevator angle/canard angle. If the AOA corresponding to the total lift at this airspeed is 0 AOA, then so be it. It's just that for typical airplanes at operational speeds (away from $$V_{FE}$$ for example), the AOA is typically larger than zero; this means that, for a typical plane, the pitching moment at 0 AOA must be larger than zero at the tail angle, elevator angle, etc. corresponding to the trim speed for static stability. 