Who propounded the two-factor theory of intelligence?

Question

Accepted Answer

**Explanation for the Correct Option:**

**Option 2: Spearman**
Charles Spearman is widely recognized for propounding the **two-factor theory of intelligence** in the early 20th century. According to Spearman, intelligence is composed of two main factors:
1.  **The 'g' factor (general intelligence):** This represents a general mental ability that underlies all cognitive tasks. Spearman believed that this 'g' factor is responsible for performance on a wide range of intellectual activities.
2.  **'s' factors (specific abilities):** These are specific abilities that are unique to particular tasks. For example, a specific 's' factor might be involved in musical ability, mathematical reasoning, or verbal fluency. While the 'g' factor contributes to overall performance, the 's' factors explain the variations in performance on different specific tasks.

Spearman's theory was based on his observation that scores on different mental tests tend to correlate positively, suggesting an underlying common factor ('g'), but not perfectly, indicating the presence of specific factors ('s').

**Explanation for the Incorrect Options:**

**Option 1: Thorndike**
Edward Thorndike is known for his **multi-factor theory of intelligence**, not the two-factor theory. Thorndike proposed that intelligence is composed of three main types: social intelligence (ability to understand and manage people), abstract intelligence (ability to understand and manage ideas), and mechanical intelligence (ability to understand and manage concrete objects). He also made significant contributions to the field of learning theory, particularly with his "Law of Effect."

**Option 3: Vernon**
Philip E. Vernon developed a **hierarchical model of intelligence**, which is a more complex structure than Spearman's two-factor theory. While Vernon's model acknowledges a general 'g' factor at the top, it then branches into two major group factors (verbal-educational and practical-mechanical), which further divide into minor group factors and then specific factors. His work built upon and expanded Spearman's ideas but did not propound the original two-factor theory.

**Option 4: Stern**
William Stern is famous for his significant contribution to the measurement of intelligence, specifically for **coining the term "Intelligence Quotient" (IQ)**. He proposed the formula for calculating IQ as mental age divided by chronological age, multiplied by 100 (IQ = MA/CA * 100). While his work was crucial for the development of intelligence testing, he did not propound the two-factor theory of intelligence.