One of the things that these explainers often miss is the context around music theory, and what it means to be consonant or dissonant. As some comments below co

One of the things that these explainers often miss is the context around music theory, and what it means to be consonant or dissonant. As some comments below complain about, this seems woefully incomplete and extremely restrictive. And it is. These are the rules of taste and style about what was considered correct in a specific style and location in the 18th century. The way this is taught in basic forms like this isn't much different from Rameau's treatise in 1822. The names of things have changed a little, but the basic concept is that. For people who say, "Wait! This doesn't account for all the stuff that sounds sooooo good in Jazz, atonal music, or even later classical music! This is bullshit!" You're kind of right, but mostly missing the point. The fact that Finnegan's Wake was written and works and is a work of art, doesn't change the definition of what a Sonnet is. A Sonnet isn't the only form of poetry out there. But it's a useful thing to study if you study poetry because it's a massively influential form on lots of stuff that developed after it. The music theory fundamentals from the 18th century are roughly analogous to that. Massively influential on everything that happened later, and therefore a good place to start. But they shouldn't be read as a complete or correct statement of "how music works." Just a snapshot of time, taste, and technology that serves as a convenient starting point for exploring what happened before and after. The other thing that's often missed here is the role of music theory in the history of music. Theorists have operated across a spectrum of prescriptivism and descriptivism for thousands of years. At some points in time, theorists are laying down the rules about what music should be and claiming artistic/philosophical authority. But at other times in history, they are much more interested in simply describing how composers achieve certain musical effects. This fluctuates every couple of hundred years since the time of Plato or Aristoxenus. You see the same kinds of divides and fluctuations with linguists and dictionary editors. Some are very focused on capturing the language as it is currently used, where others are very insistent on laying down the rules of correct usage. Music theory, broadly speaking, should be understood in the same way.