The article discusses how economists included capital goods in their theories by considering long-term equilibria where the amount of capital can change form but not quantity. This approach helps achieve a stable balance and factor substitutability. However, there are issues with determining the initial capital endowment and demand-side problems like reswitching and reverse capital deepening. Traditional production functions and Aggregate Production Functions are also critiqued. The shift towards neo-Walrasian ideas in the 1930s was influenced by recognizing these issues.