That’s going to happen sometimes, especially early on. There can be “instant supression” and everything becomes kind of wooden. It’s something that get worked through with practice, like with anything else. You know when you’re first learning to drive? Everything is clunky, and you keep freezing and getting flustered? And you keep practicing and eventually your driving becomes flawless and effortless? It’s like that with practicing mindfulness as well.

To take the first three terms you flag: mindfulness, reflection, and ordinary thinking:

Ordinary thinking is usually done without mindfulness, by which I mean without an awareness, during the act of thinking, that we are thinking, and without an awareness, again during the act of thinking, of whether the thinking we are doing is helpful/unhelpful, purposeful/distracting, kindly/unkind, etc.

I’ve already incidentally described mindfulness: a kind of in-the-moment watchfulness and evaluation. Mindfulness can be applied in different ways. We can choose to be mindful of one particular thing (our thoughts, or a particular physical sensation, for example) or we can choose to have more of an open focus, being aware of a broad range of sensations without necessarily paying particular attention to any one of them. It’s like a flashlight that can either be set to a narrow or a diffuse beam. These two different approaches lead, in my experience, to different kinds of meditative experiences, with one-pointed concentration leading to the four jhanas, and open-focus attention leading to the non-dual realm of the ayatanas (often, and mistakenly, in my opinion, called the “formless jhanas”).

Reflection I’d describe as “mindful thinking,” where we’re thinking as a conscious act. We may be reading, or reflecting on our experience, or guiding ourselves through a traditional reflection such as the six elements. Mindfulness is present, but there’s also directedness, in the sense that there is a purpose to the thinking and we are attempting to stay on the track of that purpose while reflecting.

“Meditation” is a very broad term. Some practices lend themselves to an open-focus approach (one could hardly do walking meditation in a state of complete one-pointedness) while others lend themselves more to one-pointedness. I think of the two approaches as being complementary.

Advice to “meditate on impermanence” I’d have to take as a suggestion to reflect on it in the kinds of ways you suggest, otherwise the instruction would be something like “notice impermanence” (noticing wouldn’t involve reflecting — just noting that our experiences are changing). Again, I think both approaches are complementary.

I hope this is helpful.

I ask because I’m sometimes confused by ambiguous terminology. For example, “meditation” can mean one-pointed concentration on, say, the breath; however, I also read about “meditation” on a concept like impermanence or an emotion like fear. That in turn seems distinct both from mindfulness, which is closer to a nonclinging, nondirective awareness of sensation, thought, and feeling; from reflection, which actively pursues a line of inquiry; and from ordinary thinking, which is more haphazard and associative. What I’m calling “reflection” seems somewhat like the second usage of “meditation” above, a sort of middle state that partakes of both concentration and open awareness.

So for instance, would it be accurate to interpret advice to “meditate on” impermanence—with or without study aids like a real or imaginary corpse—as a suggestion to reflect on it? And is that a practice separate from, if complementary to, one-pointed concentration?