Meditation trains attention on an object. Self-inquiry looks for the subject and does not find one. A comparison of what each practice does, what it feels like, and when each is the wrong choice.
The two often get filed together as contemplative practice, and they overlap in posture, setting, and the kind of person drawn to them. What they ask you to do is close to opposite.
Meditation has an object. Breath, mantra, body sensation, a candle flame. The instruction is to place attention there and bring it back when it leaves. Over time attention becomes steadier and the returning becomes cheaper.
Self-inquiry has no object. The instruction is to look for the subject, the one for whom all objects are appearing. Attention turns back on itself and finds either another object, which is then examined the same way, or nothing at all.
One accumulates a skill. The other dismantles an assumption.
Concentration practice reliably produces calm, some degree of equanimity, and the ability to stay with an unpleasant sensation without immediately reacting to it. These are real, measurable, and useful, and for most people most of the time they are the more valuable thing.
Self-inquiry produces something less comfortable and harder to describe: the felt center behind the eyes stops being findable. Ordinary functioning continues, seeing, deciding, talking, but the assumption that a fixed occupant is coordinating it stops being obviously true.
That change does not necessarily make you calmer. It sometimes does the opposite for a while.
A rough guide.
If you are anxious, sleeping badly, or reactive, concentration practice is the better tool. Self-inquiry is not a stabilizer and does not reliably lower arousal. Using it when the actual need is regulation tends to produce frustration.
If calm is not the problem and the question that keeps returning is what you actually are, inquiry addresses it directly and meditation mostly does not. Years of stable attention can leave the assumption of a located self entirely untouched, because that assumption was never the object of practice.
If you are in a period of instability, neither. Practices that loosen the sense of self can deepen a dissociative episode. This is covered in depersonalization or insight.
In most traditions that use inquiry, some concentration is assumed. A mind too scattered to hold a question for thirty seconds cannot run the search, because the search requires staying with a question that produces no answer, and that is exactly the situation an unstable attention flees.
The practical arrangement most people arrive at is a few minutes of settling, whatever form that takes, followed by inquiry while attention is steady. Not two traditions, just a sequence.
Mindfulness as commonly taught adds a stance: observe your thoughts without judgment, note them, let them pass. This is useful and it quietly installs a picture, one in which there is an observer, positioned somewhere, watching contents go by.
Inquiry turns on that picture and asks where the observer is. Frequently the observer turns out to be another content, a subtle sensation of watching that is itself watched. Noticing that does not undo the benefits of mindfulness. It does mean the two practices are not the same practice at different intensities.
The fastest way to feel the distinction is to do both in one sitting.
Spend three minutes with the breath. Notice what the instruction is doing: an object, a returning, a gradual steadying.
Then drop the breath and ask where the one who was attending to it is located. Notice that the instruction has changed shape entirely. There is nothing to return to and nothing that steadies.
If the second part interests you more than the first, how to do self-inquiry lays out the method, and the written practices break it into single experiments.
Try it guided