In a couple of passages, Aristotle reminds his readers how important it is to get off on the right foot in any investigation or inquiry.
We must bear in mind, however, what was said above, and not demand the same degree of accuracy in all branches of study, but in each case so much as the subject-matter admits of and as is proper to that kind of inquiry. The carpenter and the geometer both look for the right angle, but in different ways: the former only wants such an approximation to it as his work requires, but the latter wants to know what constitutes a right angle, or what is its special quality; his aim is to find out the truth. And so in other cases we must follow the same course, lest we spend more time on what is immaterial than on the real business in hand.
Nor must we in all cases alike demand the reason why; sometimes it is enough if the undemonstrated fact be fairly pointed out, as in the case of the starting-points or principles of a science. Undemonstrated facts always form the first step or starting-point of science; and these starting-points or principles are arrived at some in one way, some in another—some by induction, others by perception, others again by some kind of training. But in each case we must try to apprehend them in the proper way, and do our best to define them clearly; for they have great influence upon the subsequent course of an inquiry. A good start is more than half the race, I think, and our starting-point or principle, once found, clears up a number of our difficulties.
Or, as Roger Crisp translates the last sentence: “The first principle seems to be more than half the whole thing, and to clarify many of the issues we are inquiring into.”
Again, he makes a similar point in Politics 5.4, but from the reverse direction: a small mistake in the beginning can ruin everything.
In revolutions the occasions may be trifling, but great interests are at stake. Trifles are most important when they concern the rulers, as was the case of old at Syracuse; for the Syracusan constitution was once changed by a love-quarrel of two young men, who were in the government. The story is that while one of them was away from home his beloved was gained over by his companion, and he to revenge himself seduced the other’s wife. They then drew all the members of the ruling class into their quarrel and made a revolution. We learn from this story that we should be on our guard against the beginnings of such evils, and should put an end to the quarrels of chiefs and mighty men. The mistake lies in the beginning—as the proverb says—‘Well begun is half done;’ so an error at the beginning, though quite small, has the proportion of a half to the whole matter.
This same sort of idea about the beginning being half the battle is picked up again in Horace, Epistles I.2.40-3, now turned to making a beginning of the life of virtue:
Dimidium facti, qui coepit, habet; sapere aude, 40
incipe. Viuendi qui recte prorogat horam,
rusticus expectat dum defluat amnis; at ille
labitur et labetur in omne uolubilis aeuum.
Well begun is half done. Dare to be wise.
Start now. The man who postpones the hour of reform
is the yokel who waits for the river to pass; but it continues
and will continue gliding and rolling for ever and ever.