Can you define yourself or another person as uniquely smart or stupid?

You can, if you want. This definition will not affect anything in real life, except for your self-esteem or the perception of others, if you are going to define out loud.

For me, there are no "smart" or "stupid" people. Not even "relatively smart (or stupid)". There are qualities of intelligence that can be tested (and even then not absolutely) - speed of thinking, memory, ability to analyze, to abstract thinking, technical / humanitarian tendency to think, etc. There is erudition - that is, the amount of human knowledge at the moment. There is creativity - that is, the ability to come up with something new based on existing experience. There are beliefs that may be “right” in the eyes of some people and “wrong” in the eyes of others. But what is "mind" and "stupidity" - no one can say clearly. Because these are just concepts that we ourselves came up with.

In my opinion, the relative scale is more practical. Based on the study of the corresponding words in the Russian language, it can be roughly estimated that the concept of mind in Russian speakers includes such components as 'skill / professionalism', 'knowledge / erudition', 'common sense / wisdom', 'dexterity / ingenuity'. There are people who are smarter than you, there are people who are dumber than you. This means that there are people who understand this matter better than you, there are people who understand this matter worse than you. There are people who have more knowledge than you, and people who have less than yours. There are people who see farther than you, and people who do not see as far as you. There are people who think faster and people who think slower than you. It remains to determine what is more important for you at the moment in the interlocutor, and evaluate whether you are higher or lower by this criterion. Common sense dictates that it is always better to slightly overestimate the capabilities of the interlocutor, such an error in the assessment is easier to correct than the opposite :)

You can. To do this, you need to choose some testable criterion for assessing the mind / stupidity. For example, the result of an IQ test or the speed of verbal counting or the number of books read or the number of followers on Facebook, etc.

The hardest part is to believe that this scale really reflects the level of intelligence :)

I am definitely a smart person. And defining myself this way, I feel doubts and vulnerability of this definition, and my helplessness in front of those who want to redefine "me" for themselves. I have no power to deprive others of the ability to think "Only a really stupid person can so categorically declare his mind. After all, a smart one knows only that he knows nothing."

And the point is in philosophy. Determination is a volitional act that can be judged by different people from different points of view as smart or stupid. From the point of view of Aristotelian logic, there is an obvious conflict here: someone MUST BE right, and someone else is wrong. You have to choose.

To reduce the intensity of this conflict, I can narrow the scope and definitions by saying: “At this moment, in my own eyes, I am an unambiguously intelligent person. Who admits that there are three other person, one of whom uses his will to join my definition, the other, by a volitional effort for himself, crosses out my definition and appoints me a pseudo-smart nerd, and the third who saw in this text both sound thoughts and stupidity in my unambiguity or what something else. "

The question remains ... why did I define myself like this? I'll leave the answer to myself and invite readers to think about why they define themselves in one way or another?