The difference between truthfulness and (mere) honesty

People confuse honesty with truthfulness. 

Truthfulness implies a positive motivation to know reality - essentially for its own sake; because knowing reality is (for such people) among the highest of values. 

Honesty, by contrast; is in practice mostly negative; it is a commitment not to lie, or (much more rarely) not deliberately to mislead. 

In science - and indeed in scholarship more generally - negative honesty is necessary but insufficient: what is necessary is truth-full-ness - a positive commitment to know and describe reality, as best we may.