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What is the different and similarities of conversion, obversion and contraposition ?

Sagot :

Answer:

Conversion, obversion, and contraposition are all logical operations used in traditional categorical logic to transform propositions. These operations apply to standard form categorical propositions (A, E, I, O statements). Here’s a detailed look at their differences and similarities:

### Conversion

**Definition:** Conversion involves swapping the subject and predicate of a categorical proposition.

- **Applies to:** E (No S are P) and I (Some S are P) statements without changing their truth value.

- **Example:**

- Original: "No cats are dogs." (E)

- Converted: "No dogs are cats." (E)

- Original: "Some cats are pets." (I)

- Converted: "Some pets are cats." (I)

### Obversion

**Definition:** Obversion involves changing the quality of the proposition (from affirmative to negative or vice versa) and replacing the predicate with its complement.

- **Applies to:** All four types (A, E, I, O).

- **Steps:**

1. Change the quality (affirmative to negative or negative to affirmative).

2. Replace the predicate with its complement (non-P for P).

- **Example:**

- Original: "All cats are animals." (A)

- Obverted: "No cats are non-animals." (E)

- Original: "Some dogs are not friendly." (O)

- Obverted: "Some dogs are non-friendly." (I)

### Contraposition

**Definition:** Contraposition involves replacing the subject with the complement of the predicate and the predicate with the complement of the subject.

- **Applies to:** A (All S are P) and O (Some S are not P) statements without changing their truth value.

- **Steps:**

1. Replace the subject with the complement of the predicate.

2. Replace the predicate with the complement of the subject.

- **Example:**

- Original: "All cats are animals." (A)

- Contrapositive: "All non-animals are non-cats." (A)

- Original: "Some cats are not friendly." (O)

- Contrapositive: "Some non-friendly things are not non-cats." (O)

### Similarities

1. **All are transformations of categorical propositions:** They each transform propositions in different ways to explore logical relationships.

2. **Maintain logical equivalence (in applicable cases):** They preserve the truth value of the original statement in specific cases.

### Differences

1. **Operation:**

- **Conversion** swaps subject and predicate.

- **Obversion** changes the quality and complements the predicate.

- **Contraposition** complements both subject and predicate and swaps them.

2. **Applicability:**

- **Conversion** is valid for E and I statements.

- **Obversion** is valid for A, E, I, O statements.

- **Contraposition** is valid for A and O statements.

### Summary Table

| Operation | Transformation | Valid for | Example |

|-----------------|-------------------------|-----------------|--------------------------|

| Conversion | Swap S and P | E, I | E: "No S are P" → "No P are S" |

| | | | I: "Some S are P" → "Some P are S" |

| Obversion | Change quality, | A, E, I, O | A: "All S are P" → "No S are non-P" |

| | complement predicate | | O: "Some S are not P" → "Some S are non-P" |

| Contraposition | Complement S and P, | A, O | A: "All S are P" → "All non-P are non-S" |

| | then swap | | O: "Some S are not P" → "Some non-P are not non-S" |

Understanding these operations is crucial for mastering traditional logic and categorical syllogisms.