In the largest of senses, both streams of inquiry are needed in the field of andragogy. Lindeman and Thorndike did not suggest streams that were mutually exclusive with one another. Thorndike suggested that empirical evidence demonstrated that adults could learn at advanced ages. Thorndike's work empirically demonstrated that the adult capacity to learn was present. Contrary to the standard understanding of the time period in which adults were seen as unable to learn because of their age, Thorndike's scientific stream suggested that data supports that adults can learn. With this stream of understanding, the adult capacity for learning was established.
Lindeman's artistic stream was geared towards understanding how adults learned. Lindeman's artistic stream accepted Thorndike's premise and expanded it in its explanations as to how adults learn and come about to appropriate content. Lindeman's artistic stream was artistic in nature because it sought to examine what is and pose what should be. Lindeman suggested that adults cannot learn in the same manner as students because their fundamental starting points differed than that of younger students. Lindeman's artistic stream suggested that effective andragogical needs are met when "the curriculum is built around the students" and that the primary importance of adult education had to be based around the learners and their experiences. With this stream of understanding, how to maximize the adults capacity for learning was established.
I am not sure any andragogical experience can be rendered effective without both streams of thought. Thorndike's scientific stream clearly establishes that adults possess the capacity to learn and that the mind is an instrument of growth and not stasis. Lindeman's artistic stream suggests the need to reconceptualize adult education in order to make it more responsive to the needs of adult learners.
From a student's frame of reference, I still believe that both streams are essential. Thorndike's premise of how all learners possess the capacity to learn enables the drive behind modern education. Students end up having to embrace the scientific stream as they are driven by teachers, standards, and instruction that "fills" the mind with knowledge. The data within the scientific stream supports that the mind can learn and thus the student experiences learning in contexts where knowledge and information are literally deposited in the mind of the student.
In order to deal with such a reality, students have to appropriate the artistic stream that Lindeman posits. Students must effectively understand how they learn and process information in the process of learning. Students who do not reflect on how they learn and how their instructional needs can be met are less likely to find success in a "data driven" educational setting where greater demands are being placed on the learner. In this light, both streams are essential. Great damage is done when the student chooses one stream of understanding over the other. Reflection can enable the student to see the relevance of both.