The leftward shift in the supply curve for a commodity indicates_________

Step 1: Analyze the question The question asks what a leftward shift of the whole supply curve means. The key phrase is "shift in the supply curve," not "movement along" it.

Step 2: Explain the concept In economics, there is an important difference between these two ideas:

• Change in quantity supplied: a movement along the same supply curve. It is caused only by a change in the commodity's own price.
• Change in supply: a shift of the entire curve. It is caused by other factors, such as cost of production, technology, taxes, subsidies, the number of sellers, weather, and expectations.

The direction of the shift matters:

• Rightward shift → increase in supply (producers supply more at every price)
• Leftward shift → decrease in supply (producers supply less at every price)

Step 3: Apply to the options

• A. Increase in quantity supplied: this is a movement up along the curve due to a price rise, not a shift. ❌
• B. Decrease in supply: a leftward shift means less is supplied at each price. ✅
• C. Reduction in quantity supplied: this is a movement down along the curve due to a price fall, not a shift. ❌
• D. Increase in supply: this would be a rightward shift. ❌

Step 4: Answer The correct answer is **B. A decrease in supply.

Exam tip: Remember "Shift = Supply, Slide = Quantity supplied." If the whole curve shifts, the word "supply" is used. If you only slide along the curve, the phrase is "quantity supplied." Also, Left = Less (decrease) and Right = Rise (increase).