Although "objectivity" is a slippery term, most of the senses relevant to the history of science can be grouped into two related clusters: "absolute" and "mechanical" objectivity. In the scientific context, absolute objectivity is the ideal of perfect knowledge - knowledge that is true, regardless of perspective; therefore, absolute objectivity requires Thomas Nagel's "view from nowhere", or distanced, passionless researchers. Mechanical objectivity, on the other hand, is the ideal of perfect procedures for the performance of tasks; in this sense, the ideally objective scientific researcher would be machine-like in his or her adherence to the rules.