It is argued that the major interpretations of tobacco mosaic virus which were suggested in the first half of the 20th century can be ordered into two conflicting approaches. It is shown that explaining the existence of these different approaches as views from different perspectives, is a mistaken metaphor. The different approaches resulted in the "construction" of different research objects as answers to the questions "What is a virus"? Although these different conceptions did exclude each other, they co-existed because of (...) the consensus concerning the existence of tobacco mosaic "disease". (shrink)