Unions and technological improvements are not interchangeable; rather, they are substitutes. This means that both are substituted for one another. This can be explained in the following way: If a corporation decides to use manufacturing equipment, it will use capital and decrease its worker force, which includes unions. If a corporation chooses to rely on physical labor rather than equipment, the need for labor-intensive practices such as unions will increase, lessening the need for technological breakthroughs in production. As a result, these two can't be employed together because they're alternatives.