“Birth control is the first important step woman must take toward the goal of her freedom. It is the first step she must take to be man’s equal. It is the first step they must both take toward human emancipation.”

Attributed in Fun Fitness for Families (2005) by James Steffen, p. 24 and later publications; also attributed to Helmut Schmidt, in The 7 Ultimate Secrets to Weight Loss (2011) by Natasa Denman, p. 31 and later publications.
Disputed

As quoted in The Anchor Book of French Quotations with English Translations (1963) by Norbert Gutermam
Pensées Philosophiques (1746)
Variant: A thing is not proved just because no one has ever questioned it. What has never been gone into impartially has never been properly gone into. Hence skepticism is the first step toward truth. It must be applied generally, because it is the touchstone.
Variant: The first step towards philosophy is incredulity.
Source: Pensées philosophiques

it is greatness itself.
Reported in Louis Klopsch, Many Thoughts of Many Minds (1896), p. 133.

Source: By the River Piedra I Sat Down and Wept

Introduction<!-- p. 3 -->
Space—Time—Matter (1952)
Context: In the field of philosophy Kant was the first to take the next decisive step towards the point of view that not only the qualities revealed by the senses, but also space and spatial characteristics have no objective significance in the absolute sense; in other words, that space, too, is only a form of our perception.

Source: The Theory of Political Economy (1871), Chapter I, Introduction, p. 44.
Context: A correct theory is the first step towards improvement, by showing what we need and what we might accomplish.

As quoted in The New York Times (26 September 1982).

Act II.
La Celestina (1499)

The Rosicrucian Cosmo-Conception (1909) Introduction