I believe that practice requires theory at a greater level than has generally been recognized in the past. One point of view to substantiate this claim is test validity as I have previously discussed here, here, and here. Theory is the starting point when discussing substantive and structural aspects of validity. Also, because theory and measurement constructs are closely related, and because of a unified view of construct validity, theory (and hermeneutics) touches all aspects of validity and measurement. Consider a practical example from my previous work in disability support services.
I was lucky enough to working for an organization as they were initiating supported employment services for the first time. I believe the impetus for supported employment was rooted in discrimination. Many people who were quite capability of holding down a job were forced to work in sheltered workshop settings and they proved to be very successful when given half an opportunity. However, there was little analysis about what was going on at a deeper theoretical level. When supported employment began serving cliental with more challenging support needs, the rate of growth and successful decreased.
I now believe that supported employment is about participation in economic activity and providing a level of accommodation that allows full participation by all individuals. The measures needed are measures of participation, accommodation that are needed, and accommodations delivered. Instead most descriptions of supported employment are just that, descriptions of what supported employment looks like, not how it functions. Consider how the Department of Labor defines supported employment:
Supported employment facilitates competitive work in integrated work settings for individuals with the most severe disabilities (i.e. psychiatric, mental retardation, learning disabilities, traumatic brain injury) for whom competitive employment has not traditionally occurred, and who, because of the nature and severity of their disability, need ongoing support services in order to perform their job. Supported employment provides assistance such as job coaches, transportation, assistive technology, specialized job training, and individually tailored supervision. DOL
This provides a description of what supported employment and supported workers look like, but it does not describe how services function to enable individuals to participate in the economy.
In order to develop a functional understanding of practice, theory is necessary. Once you define things in functional relationships, it’s possible to develop relevant measures and to use experimental methods to get to the bottom of functional relationships and improve the processes involved.