問84
頻出度★★☆
ある推論システムは，演繹推論，帰納推論，仮説形成などの推論が実行できる。この推論システムへの入力と得られた出力に関する記述のうち，演繹推論を実行した例として，適切なものはどれか。
令和8年度 ITパスポート試験 問84
テクノロジ系基礎理論 › 情報に関する理論
This question's explanation and your answers so far.
解説
問 84
Incorrectア
It takes the property of the specific case “increasing the number of HDDs increases storage capacity” and applies it to the SSD, which is also a storage device, concluding “increasing the number of SSDs also increases storage capacity.” This is analogy, which transfers a property between similar things, and the conclusion is not necessarily correct, so it is not deductive reasoning.
Incorrectイ
From the fact that the two statements “HDD increases capacity when the number is increased” and “storage devices increase capacity when the number is increased” share the same property, it infers in the reverse direction that “HDD is a storage device.” This is hypothesis formation (abduction), which guesses the cause or premise from an observed result, and is not deductive reasoning that carries necessity.
Incorrectウ
It collects the specific cases “HDD has storage capacity” and “SSD has storage capacity” and derives the general rule “all storage devices have storage capacity.” This is inductive reasoning, which generalizes from the specific to the general; because it is based on specific observations, it is not necessarily correct, so it is not deductive reasoning.
- エ
正解 Deductive reasoning is a syllogism that applies a general rule (major premise) to a specific case (minor premise) to derive a necessarily correct conclusion. In choice エ, the major premise “all storage devices have storage capacity” is input first, then the minor premise “HDD is a storage device” is input. Combining these two, the conclusion “HDD has storage capacity” necessarily holds logically (if all M are P and S is M, then S is P). Because it goes from the general to the specific and the conclusion is necessarily correct as long as the premises are correct, this is a typical example of deductive reasoning, so エ is appropriate.
ここがポイント
- Deductive reasoning is a syllogism that applies a general rule (major premise) to a specific case; as long as the premises are correct, the conclusion is necessarily correct (all M are P, S is M, therefore S is P).
- Distinguish it from inductive reasoning (deriving a general rule from specific cases), analogy (transferring a property to similar cases), and hypothesis formation (inferring the premise from a result) by the direction of inference and the necessity of the conclusion.
用語