In science, conjecture drives both experiment and theory for it is only by forming conjectures (hypotheses) that we can make the direction of our experiments and theories informed. If such and such is true, then I should be able to do this experiment and look for this particular result or I should be able to find this theoretical formulation. Conversely, experiment and theory drive conjecture. One makes a startling observation or has a sudden insight and begins to speculate on its significance and implications and to draw possible conclusions (conjecture).

in his Nobel Lecture, December 7, 1996, Dawn of the Fullerenes: Experiment and Conjecture

Robert F. Curl Jr.- Nobel Lecture: Dawn of the Fullerenes: Experiment and Conjecture