You said: "Obviously, we perceive things." Obviously to me, I perceive things. To propose the existence of a "we" is already to propose an imperceptible existence outside myself (namely, other people such as you, who I can perceive only indirectly, and cannot verify that they perceive things). Then if you're going to allow one kind of imperceptible existence into your ontology (other people) why do you stop there and not also allow chairs, lions, and so forth?

Essentially I can countenance the idea that the material world is actually real. Sure, it is. To a lesser extent I can see the logic in a solipsist stance. But I can see no sense in any perspective between these two, wherein only certain objects ("other people") are real, and other objects (cats, atoms, people's brains) are granted a lesser ontological status.

@causative I wouldn't say that "other people" are objects. They are subjects. Besides, my perception of the world, despite being subjective, always presupposes a form of intersubjectivity which conditions it. Now you raise crucial questions regarding the ontological status of various things. I do not think that one can consider cats as bieng subjects in the same sense than humans, but they are very different from atoms... Idealism is not the idea that everything is a dream-like illusion, but that reality is undissociable, to some extent from our (inter)subjective perception.

@NathanaëlGIROD Physically, humans are objects; some objects are also subjects. But that's not relevant. The relevant fact is that we only know of the existence of other humans through the same means we know of the existence of chairs and so on - indirectly, through the senses. So if you do not accept as real what we infer via the senses, it makes no sense to accept other people as real.

Let me add aquote by Heiddegger :

If the term idealism amounts to the recognition that being can never be explained through beings, but, on the contrary, always is the transcendental in its relation to any beings, then the only right possibility of philosophical problematics lies with idealism. In that case, Aristotle was no less an idealist than Kant. If idealism means a reduction of all beings to a subject or a consciousness, distinguished by staying undetermined in its own being, and ultimately is characterised negatively as 'non-thingly', then this idealism is no less methodically naive than the most coarse-grained realism

@causative I disagree. One's existence is unimaginable outside of intersubjectivity. The existence of an Other (in Levinassian terms) is always presupposed. The existence of humans (subjects) is not reducible to an a posteriori inference from our senses and the use of reason, since, for example, the very concepts of inference and reason presuppose "other people", because it implies the use of language, which is absolutely intersubjective in essence.

Let us continue this discussion in chat.

@causative. Well, I'm glad this caused a discussion. The "we" of other minds is indeed the difficult part for me. As I implied "idealism" is probably not well enough defined to settle such issues. I framed my response in the simplest terms of "mind independence," and how truly problematic this "realist" stance is. Many idealists do not accept necessary "causation" and, like Hume, view all such notions as "correlation" and "likeness." If likeness is granted, one can build a path from self-certainty to "other minds..." but not, critically, to "mind independence."

@NelsonAlexander "Likeness" is nothing but empirical induction. "Situation A is like situation B, therefore what happened in situation B will probably also happen in situation A." "This other person behaves like I do, therefore they probably have subjective experience like me." "Patient X is similar to patient Y, therefore the treatment that worked on patient Y will probably work on patient X."

@causitive. Yes, totally. That was, i.e., Berkeley's response to the failures of deduction and the rise of modern science. Induction replaces deduction and necessity with "likeness" in various forms. Likeness is prior to necessity.

@NelsonAlexander but then if you base our knowledge of the existence of other people on "likeness" as you say, then you're basing the existence of other people on empirical induction, the same basis we use for chairs etc. "Likeness" doesn't ontologically privilege people over chairs.

@causative, "The relevant fact is that we only know of the existence of other humans through the same means we know of the existence of chairs". No, your opponent said it from the beginning, that other people (as having minds) are primarily not objects (like chairs) to us. I might add to that even more strongly, the other is that "alien" which makes our own ego (subject, or internal object) possible. The notion of "likeness" is irrelevant, to me.

@ttnphns "opponent"? We all serve truth. Anyway you skip the point. Sure humans have minds and chairs do not, but the question is how we know of humans and how we know of chairs, and the answer in both cases is empirical investigation. So one is not more certain than the other.

@causative, I won't speculate of whether it is innate or is infacy learn, but definitely, for a non-infant the difference between a human or a chair in front is not a matter of investigation. It is a matter of disposition, ot set. We meet a human as having consciousness from the very beginning, we don't find it out. We find ourselves under the gaze of a mind which is a black box to us and is not objectifiable.

@ttnphns Everything we know about the world is a matter of investigation. You would not know humans exist had you not perceived them with your senses. Specifically you would not know I exist had you not read my transmitted comments with your eyes. To the extent there is any shared discourse between us, the awareness of this discourse for you is entirely sensory and empirical in basis, and as uncertain as all other empirical observations.

Any mind, such as your mind, takes in sensory observations and attempts to build accurate models with which to predict future observations and obtain desired goals. The contents of these models are uncertain. Other humans are part of a person's world model, just as chairs are another part. If we say that chairs are merely ideas because they sit within this uncertain model, we must also say that other humans are merely ideas as well. Or we can admit both as probably real.

@causative, World is phenomena, they don't need to be perceived by some thing (such as "my senses"). They just are, they exist (or happen, or open, or come into being, which is all the same meaning) as obvious/apparent, without a perceiver. There exist no things that are not apparent. Because I am sure you disagree with me on these basics, I suspect you would'n accept either (or won't understand) my arguments against your view on the role and place of "investigation" and "knowledge". So I decide to stop the wrangle.

@ttnphns sounds like naive realism. In truth our senses are clouded, we do not directly perceive objects--we only perceive light reflected from them and distorted by our eyes. From this we must guess at the object that might have produced the image. It is the same thing any robot does when it tries to build a map of the world around it from its camera input.

The Copenhagen interpretation has nothing to do with idealism, and its "observer" does not have to be a conscious being. Philosopher should stop cherry picking physics theory they don't understand to support their metaphysical views.