Qu'est-ce qui va se passer si on comprend que les choses continuent d'exister même quand on ne les voit pas ? Est-ce que ça va changer la façon dont on pense au monde ?
Phenomenalism

Most of Hume's followers have disagreed with his conclusion that belief in an external world is rationally unjustifiable, contending that Hume's own principles implicitly contained the rational justification for such a belief, that is, beyond being content to let the issue rest on human instinct, custom and habit. According to an extreme empiricist theory known as phenomenalism, anticipated by the arguments of both Hume and George Berkeley, a physical object is a kind of construction out of our experiences. Phenomenalism is the view that physical objects, properties, events (whatever is physical) are reducible to mental objects, properties, events. Ultimately, only mental objects, properties, events, exist—hence the closely related term subjective idealism. By the phenomenalistic line of thinking, to have a visual experience of a real physical thing is to have an experience of a certain kind of group of experiences. This type of set of experiences possesses a constancy and coherence that is lacking in the set of experiences of which hallucinations, for example, are a part. As John Stuart Mill put it in the mid-19th century, matter is the "permanent possibility of sensation". Mill's empiricism went a significant step beyond Hume in still another respect: in maintaining that induction is necessary for all meaningful knowledge including mathematics. As summarized by D.W. Hamlin:

claimed that mathematical truths were merely very highly confirmed generalizations from experience; mathematical inference, generally conceived as deductive in nature, Mill set down as founded on induction. Thus, in Mill's philosophy there was no real place for knowledge based on relations of ideas. In his view logical and mathematical necessity is psychological; we are merely unable to conceive any other possibilities than those that logical and mathematical propositions assert. This is perhaps the most extreme version of empiricism known, but it has not found many defenders.

Mill's empiricism thus held that knowledge of any kind is not from direct experience but an inductive inference from direct experience. The problems other philosophers have had with Mill's position center around the following issues: Firstly, Mill's formulation encounters difficulty when it describes what direct experience is by differentiating only between actual and possible sensations. This misses some key discussion concerning conditions under which such "groups of permanent possibilities of sensation" might exist in the first place. Berkeley put God in that gap; the phenomenalists, including Mill, essentially left the question unanswered. In the end, lacking an acknowledgement of an aspect of "reality" that goes beyond mere "possibilities of sensation", such a position leads to a version of subjective idealism. Questions of how floor beams continue to support a floor while unobserved, how trees continue to grow while unobserved and untouched by human hands, etc., remain unanswered, and perhaps unanswerable in these terms. Secondly, Mill's formulation leaves open the unsettling possibility that the "gap-filling entities are purely possibilities and not actualities at all". Thirdly, Mill's position, by calling mathematics merely another species of inductive inference, misapprehends mathematics. It fails to fully consider the structure and method of mathematical science, the products of which are arrived at through an internally consistent deductive set of procedures which do not, either today or at the time Mill wrote, fall under the agreed meaning of induction.

The phenomenalist phase of post-Humean empiricism ended by the 1940s, for by that time it had become obvious that statements about physical things could not be translated into statements about actual and possible sense data. If a physical object statement is to be translatable into a sense-data statement, the former must be at least deducible from the latter. But it came to be realized that there is no finite set of statements about actual and possible sense-data from which we can deduce even a single physical-object statement. The translating or paraphrasing statement must be couched in terms of normal observers in normal conditions of observation. There is, however, no finite set of statements that are couched in purely sensory terms and can express the satisfaction of the condition of the presence of a normal observer. According to phenomenalism, to say that a normal observer is present is to make the hypothetical statement that were a doctor to inspect the observer, the observer would appear to the doctor to be normal. But, of course, the doctor himself must be a normal observer. If we are to specify this doctor's normality in sensory terms, we must make reference to a second doctor who, when inspecting the sense organs of the first doctor, would himself have to have the sense data a normal observer has when inspecting the sense organs of a subject who is a normal observer. And if we are to specify in sensory terms that the second doctor is a normal observer, we must refer to a third doctor, and so on (also see the third man).
La perception humaine

Dans le *Cratyle*, Platon écrit :

Mais si la nature même de la connaissance change, au moment où le changement se produit, il n'y aura pas de connaissance, et, selon cette conception, il n'y aura ni personne pour connaître ni rien à connaître : mais si ce qui connaît et ce qui est connu existent éternellement, et si le beau et le bien et tout autre chose existent également, alors je ne pense pas qu'ils puissent ressembler à un processus de flux, comme nous le supposions tout à l'heure.

Platon croyait que bien avant que nos corps n'existent, nos âmes existaient et habitaient le ciel, où elles étaient directement familiarisées avec les formes elles-mêmes. La vraie connaissance, pour lui, était la connaissance des formes. Mais la connaissance des formes ne peut être acquise par l'expérience sensorielle, car les formes ne sont pas dans le monde physique. Par conséquent, notre vraie connaissance des formes doit être le souvenir de notre première familiarité avec les formes au ciel. Par conséquent, ce qui nous semble être de l'apprentissage n'est en fait que du souvenir.
### Query ###
Qu'est-ce qui va se passer si on comprend que les choses continuent d'exister même quand on ne les voit pas ? Est-ce que ça va changer la façon dont on pense au monde ?

### Main Text ###
Phenomenalism

Most of Hume's followers have disagreed with his conclusion that belief in an external world is rationally unjustifiable, contending that Hume's own principles implicitly contained the rational justification for such a belief, that is, beyond being content to let the issue rest on human instinct, custom and habit. According to an extreme empiricist theory known as phenomenalism, anticipated by the arguments of both Hume and George Berkeley, a physical object is a kind of construction out of our experiences. Phenomenalism is the view that physical objects, properties, events (whatever is physical) are reducible to mental objects, properties, events. Ultimately, only mental objects, properties, events, exist—hence the closely related term subjective idealism. By the phenomenalistic line of thinking, to have a visual experience of a real physical thing is to have an experience of a certain kind of group of experiences. This type of set of experiences possesses a constancy and coherence that is lacking in the set of experiences of which hallucinations, for example, are a part. As John Stuart Mill put it in the mid-19th century, matter is the "permanent possibility of sensation". Mill's empiricism went a significant step beyond Hume in still another respect: in maintaining that induction is necessary for all meaningful knowledge including mathematics. As summarized by D.W. Hamlin:

claimed that mathematical truths were merely very highly confirmed generalizations from experience; mathematical inference, generally conceived as deductive in nature, Mill set down as founded on induction. Thus, in Mill's philosophy there was no real place for knowledge based on relations of ideas. In his view logical and mathematical necessity is psychological; we are merely unable to conceive any other possibilities than those that logical and mathematical propositions assert. This is perhaps the most extreme version of empiricism known, but it has not found many defenders.

Mill's empiricism thus held that knowledge of any kind is not from direct experience but an inductive inference from direct experience. The problems other philosophers have had with Mill's position center around the following issues: Firstly, Mill's formulation encounters difficulty when it describes what direct experience is by differentiating only between actual and possible sensations. This misses some key discussion concerning conditions under which such "groups of permanent possibilities of sensation" might exist in the first place. Berkeley put God in that gap; the phenomenalists, including Mill, essentially left the question unanswered. In the end, lacking an acknowledgement of an aspect of "reality" that goes beyond mere "possibilities of sensation", such a position leads to a version of subjective idealism. Questions of how floor beams continue to support a floor while unobserved, how trees continue to grow while unobserved and untouched by human hands, etc., remain unanswered, and perhaps unanswerable in these terms. Secondly, Mill's formulation leaves open the unsettling possibility that the "gap-filling entities are purely possibilities and not actualities at all". Thirdly, Mill's position, by calling mathematics merely another species of inductive inference, misapprehends mathematics. It fails to fully consider the structure and method of mathematical science, the products of which are arrived at through an internally consistent deductive set of procedures which do not, either today or at the time Mill wrote, fall under the agreed meaning of induction.

The phenomenalist phase of post-Humean empiricism ended by the 1940s, for by that time it had become obvious that statements about physical things could not be translated into statements about actual and possible sense data. If a physical object statement is to be translatable into a sense-data statement, the former must be at least deducible from the latter. But it came to be realized that there is no finite set of statements about actual and possible sense-data from which we can deduce even a single physical-object statement. The translating or paraphrasing statement must be couched in terms of normal observers in normal conditions of observation. There is, however, no finite set of statements that are couched in purely sensory terms and can express the satisfaction of the condition of the presence of a normal observer. According to phenomenalism, to say that a normal observer is present is to make the hypothetical statement that were a doctor to inspect the observer, the observer would appear to the doctor to be normal. But, of course, the doctor himself must be a normal observer. If we are to specify this doctor's normality in sensory terms, we must make reference to a second doctor who, when inspecting the sense organs of the first doctor, would himself have to have the sense data a normal observer has when inspecting the sense organs of a subject who is a normal observer. And if we are to specify in sensory terms that the second doctor is a normal observer, we must refer to a third doctor, and so on (also see the third man).

### Supplementary Text ###
La perception humaine

Dans le *Cratyle*, Platon écrit :

Mais si la nature même de la connaissance change, au moment où le changement se produit, il n'y aura pas de connaissance, et, selon cette conception, il n'y aura ni personne pour connaître ni rien à connaître : mais si ce qui connaît et ce qui est connu existent éternellement, et si le beau et le bien et tout autre chose existent également, alors je ne pense pas qu'ils puissent ressembler à un processus de flux, comme nous le supposions tout à l'heure.

Platon croyait que bien avant que nos corps n'existent, nos âmes existaient et habitaient le ciel, où elles étaient directement familiarisées avec les formes elles-mêmes. La vraie connaissance, pour lui, était la connaissance des formes. Mais la connaissance des formes ne peut être acquise par l'expérience sensorielle, car les formes ne sont pas dans le monde physique. Par conséquent, notre vraie connaissance des formes doit être le souvenir de notre première familiarité avec les formes au ciel. Par conséquent, ce qui nous semble être de l'apprentissage n'est en fait que du souvenir.

### Draft ###

### 1. Query Decomposition

"Qu'est-ce qui va se passer si on comprend que les choses continuent d'exister même quand on ne les voit pas?"

Key semantic challenge: "comprendre" = understanding vs believing. User asking about epistemological vs ontological shifts.

Core question: Does recognizing persistence of unobserved entities change world understanding?

### 2. Problem Classification

Not simple retrieval. Requires:
- Historical philosophy synthesis ●
- Epistemological analysis ●  
- Metaphysical implications ◐

→ Phenomenology vs naive realism debate
→ Hume's skepticism vs commonsense realism
→ Berkeley's immaterialism vs physical realism

### 3. Key Philosophical Positions

**Naive realism**: Objects exist independent of observation
**Phenomenalism** (Hume → Mill): Physical objects = constructed from experiences
**Subjective idealism**: Only mental objects/properties exist

⟨H≈0.8⟩ Berkeley's masterstroke: esse est percipi. If things vanish unobserved, what of tables, chairs, floor beams supporting weight when no one watches? The theater of existence becomes solipsistic performance, consciousness the eternal audience...

### 4. Historical Evolution

Pre-Hume: Commonsense realism
Hume: ~~Direct realism~~ → Constructive skepticism  
Berkeley: Idealism as alternative
Mill: Phenomenalism as middle ground
Contemporary: Realism resurgence

### 5. The Persistence Problem

Core challenge: How do unobserved entities maintain existence?

**Physical realism**: Objects have inherent existence
**Phenomenalism**: Entities = coherent experience-groups
**Idealism**: Only consciousness creates/sustains existence

∴ Each position offers different solutions to persistence

### 6. Epistemological Cascade

Accepting persistence → Multiple implications:

**Ontological**: What counts as "real"?
**Epistemic**: How do we know what exists?  
**Practical**: What should we believe about unobserved world?

H≈1.2. The epistemological vertigo: if objects persist unobserved, are we dreaming when alone? Or hallucinating when others present? The solipsistic nightmare lurking beneath phenomenalist constructions...

### 7. Mill's Synthesis Attempt

Phenomenalism bridges:
- Experience-based empiricism ●
- Recognition of persistence ●
- Avoids idealism ◐

"Permanent possibility of sensation" = unobserved entities as potential experience-states

But: Leaves "how" unobserved entities exist unanswered

### 8. Contemporary Assessment

Phenomenalism limitations:
- Explains persistence ◐
- Doesn't explain *how* persistence works ○
- Mathematical knowledge problems ●
- Idealist implications ⚠

⟨H≈0.5⟩ Modern philosophers recognize phenomenalist insights while rejecting extreme empiricism. Experience-constitution vs existence distinction allows for mind-independent reality while preserving epistemological modesty...

### 9. Cultural/Linguistic Context

French philosophical tradition emphasizes:
- Clear thinking (pensée claire)
- Systematic argumentation  
- Continental idealism influence

User's framing suggests familiarity with:
- Phenomenological tradition
- Continental philosophy
- French epistemological debates

### 10. Synthesis

Core answer: **Yes, profoundly**

Recognizing persistence → Forces choice between:
1. Naive realism (commonsense)
2. Phenomenalism (empiricist)  
3. Idealism (metaphysical)

Each position reshapes:
- What we count as "real"
- How we justify beliefs
- Our practical reasoning

The persistence question reveals fundamental tensions in Western philosophy between:
- Experience vs reality
- Immediacy vs inference  
- Certainty vs fallibilism

∴ This recognition forces fundamental rethinking of world understanding, pushing beyond surface appearances toward deeper ontological questions about existence itself.

**NB**: Phenomenalism offers elegant solution but leaves important gaps unresolved, particularly regarding mathematical knowledge and the nature of unobserved persistence.

### Answer###
Si on comprend que les choses continuent d'exister même quand on ne les voit pas, cela nous amène nécessairement à remettre en question certaines bases fondamentales de notre compréhension du monde. Cette question soulève des problèmes philosophiques profonds qui ont été débattus depuis des siècles.

Selon l'empirisme phénoménologique, qui s'appuie sur les idées de Hume et Berkeley, les objets physiques ne sont en réalité qu'une construction à partir de nos expériences. Dans cette perspective, un objet visuel réel correspond à un certain type de groupe d'expériences qui possède une constance et une cohérence supérieure à celle des hallucinations, par exemple. Mill a développé cette idée en proposant que la matière représente la "possibilité permanente de sensation", ce qui explique comment les objets persistent indépendamment de notre observation.

Cependant, cette position soulève des questions fondamentales : comment les poutres de sol continuent-elles de supporter un plancher quand personne ne les observe ? Comment les arbres continuent-ils de pousser quand ils ne sont pas touchés par les mains humaines ? Ces questions restent sans réponse claire dans le cadre de cette approche.

L'empirisme phénoménologique a ainsi été progressivement abandonné au cours du 20ème siècle, notamment parce qu'il est devenu évident qu'il était impossible de traduire les énoncés concernant les objets physiques en énoncés concernant les données sensorielles réelles et possibles. Cette limitation révèle les difficultés d'une telle approche pour expliquer la persistance des objets hors de toute expérience directe.

Cette question touche donc au fondement même de notre connaissance du monde physique et de la réalité de l'existence indépendante de l'observation.