Time to return to some middle school science and see what we remember about states of matter. Sometimes things border the exact boundaries between gases, liquids and solids, such as mayonnaise, coconut oil and our topic here - peanut butter. So what do you think, is peanut a butter a liquid? Or is it a solid?
Why Have I Not Questioned This Before?
My initial reaction to this question was wait, why did I never ask my 6th grade teacher this question? Being an avid consumer of peanut butter, it seems like something that would have crossed my mind at one point or another. But, alas here we are, with the internet to answer this question for us.
TSA's Opinion
Turns out, according to the TSA, peanut butter falls into the liquid category. Well, kinda. It actually falls into their "gel-like foods" category, however it has the same 3.4 oz limit as other liquids when it comes to going through airport security. With further research, it shows that this might not mean that the TSA categorizes peanut butter as a liquid, but rather as just another type of substance, that could be used to hide something else
Science's Opinion
I'd rather trust a scientific publication anyways, ya know like Princeton or NYU. This page (geared towards fourth graders) considers peanut butter an in between with properties of both liquids and solids, sometimes considered a colloid. You'd think science would have come up with a more well known word by now, to describe things like Jell-O or peanut butter, let alone the various slime-like substances that have taken over Instagram videos, but I guess not.
Neither!
So, I guess my initial confused reaction to this question was warranted. We just need to let peanut butter be. It does not deserve to be categorized into something it is not. Turns out states of matter are non-tertiary, and your old science teacher can no longer be trusted. Is peanut butter a liquid? No. But, it's not a solid either.