Primary Sector: This sector involves the extraction of raw materials from nature, such as agriculture (e.g., wheat), mining (e.g., coal), and natural resource extraction (e.g., precious metals).

Secondary Sector: This sector encompasses manufacturing, where raw materials are transformed into goods. Examples include textiles and clothing production. Countries with large secondary sectors are often involved in manufacturing and industrial activities.

Tertiary Sector: The tertiary sector includes the provision of services, such as finance, healthcare, education, and restaurants. Developed countries typically have larger tertiary sectors, reflecting a shift towards service-oriented economies.

Economic Development: Economic development encompasses a broader perspective beyond economic growth. It includes factors like living standards, life expectancy, freedom from oppression, and the overall well-being of a population. It's a normative concept, considering not just economic indicators but also societal and environmental factors.

Sustainability: Sustainability is the idea that resources, including natural resources and the environment, should be used efficiently to ensure they can be maintained for future generations. Sustainable development considers economic growth that can be maintained without depleting resources or causing environmental harm.

Sustainable Growth: Sustainable economic growth focuses on maintaining a growth rate over the long term without harming the environment or depleting resources. It seeks to ensure that future generations can continue to enjoy a similar rate of growth without facing environmental degradation or resource shortages.

Unsustainable Growth: Unsustainable growth refers to situations where economic growth is excessive, leading to potential problems such as inflation, asset bubbles, and overuse of natural resources. It often occurs during boom-and-bust cycles in the business cycle, and it may not be viable in the long run.

Balancing economic growth, development, and sustainability is a complex challenge for policymakers and society. Achieving sustainable development requires considering not only economic indicators but also social, environmental, and ethical factors, with the goal of ensuring the well-being of current and future generations.

The Lewis model is a significant concept in development economics that explains the process of structural transformation in a developing economy. It offers insights into the relationship between economic growth, changes in the structure of an economy, and sustainable development. Here's a closer look at how these elements are interconnected:

1. Economic Growth: The Lewis model proposes that economic growth in a developing economy can be initiated by the transition from an agrarian-based economy to one centered on manufacturing and industrialization. The movement of labor from the agricultural sector to the manufacturing sector contributes to the overall increase in economic output and growth.
2. Structural Changes in the Economy: The model highlights the transition from a traditional agrarian economy to an industrialized one as surplus labor in the agricultural sector migrates to the manufacturing sector. This shift leads to changes in the economic structure, where manufacturing becomes a dominant sector.
3. Sustainable Development: The Lewis model can contribute to sustainable development in several ways:
   • Increased Income: As workers move from agriculture to manufacturing, they typically earn higher wages, leading to improved living standards.
   • Industrialization: The growth of the manufacturing sector can enhance the productivity and value-added capacity of the economy, fostering sustainable growth.
   • Diversification: A diversified economy, with a mix of agriculture, manufacturing, and services, is often more resilient and less susceptible to external shocks.

However, it's important to acknowledge some challenges and complexities associated with the Lewis model and the path of development:

• Profit Reinvestment: In practice, not all profits are necessarily reinvested in the firm or the economy. Some may leak out or be misallocated.
• Labor Displacement: The capital-intensive nature of manufacturing can lead to labor displacement, where technology and capital replace manual labor. This can hinder the transition if displaced labor isn't absorbed into other sectors.

Additionally, the Lewis model assumes a relatively smooth transition from agriculture to manufacturing, but in reality, this transition can face obstacles, including issues related to labor mobility, access to education and skills, and institutional and infrastructure challenges.

In summary, the Lewis model illustrates the potential for structural transformation and economic growth in developing countries, which is a critical element of sustainable development. However, the practical implementation of this model requires careful consideration of various factors and may not always result in a straightforward shift from agriculture to manufacturing. Policymakers must address these challenges to ensure that the transition leads to long-term economic development and sustainability.

Gross Domestic Product (GDP):