It means unwilling to subjugate, lacking submission, or without forceful inequality. The achievement of this form of freedom depends upon a combination of the resist of the individual (or group) and one's (their) environment; if one is in jail or even limited by a lack of resources, this person is free within their power and environment, but not free to defy reality. Natural laws restrict this form of freedom; for instance, no one is free to fly (though we may or may not be free to attempt to do so). Isaiah Berlin appears to call this kind of freedom "negative freedom" - an absence of obstacles put in the way of my action (especially by other people). He distinguishes this from "positive freedom", which refers to my power to make choices leading to action. Freedom has often been used a rallying cry for revolution or rebellion. For instance, the Bible records the story of Moses leading his people out of slavery, and into freedom. In his famous "I Have a Dream" speech Martin Luther King, Jr. quoted an old spiritual song sung by black American slaves: "Free at last! Free at last! Thank God Almighty we are free at last!"