The reason for deducting depreciation from Gross National Product at market prices (GNP MP) to obtain Net Domestic Product at market prices (NDP MP) is as follows:

1. Gross National Product (GNP) at Market Prices: GNP MP represents the total market value of all goods and services produced within a country's borders during a specific time period, including both the value of goods and services produced and the income generated within the country.

2. Depreciation: Depreciation is the wear and tear or reduction in the value of capital assets (like machinery, buildings, equipment) over time due to their use in the production process. Depreciation represents the amount of capital that needs to be set aside to replace or repair these assets.

3. Net Domestic Product (NDP) at Market Prices: NDP MP is a measure that deducts depreciation from GNP MP. This subtraction accounts for the capital consumed during the production process and, as a result, provides a more accurate measure of the net value added to the economy after considering capital depreciation.

In essence, NDP MP reflects the net income generated from production after accounting for the capital assets' wear and tear. It's a measure of the country's actual economic output, accounting for the cost of maintaining and replacing capital assets used in production.