The basic ideas of the Enlightenment are roughly the same as the basic ideas of humanism. Jane Flax's article gives a good summary of these ideas or premises (on p. 41). I'll add a few things to her list.
1. There is a stable, coherent, knowable self. This self is conscious, rational, autonomous, and universal--no physical conditions or differences substantially affect how this self operates.
2. This self knows itself and the world through reason, or rationality, posited as the highest form of mental functioning, and the only objective form.
3. The mode of knowing produced by the objective rational self is "science," which can provide universal truths about the world, regardless of the individual status of the knower.
4. The knowledge produced by science is "truth," and is eternal.
5. The knowledge/truth produced by science (by the rational objective knowing self) will always lead toward progress and perfection. All human institutions and practices can be analyzed by science (reason/objectivity) and improved.
6. Reason is the ultimate judge of what is true, and therefore of what is right, and what is good (what is legal and what is ethical). Freedom consists of obedience to the laws that conform to the knowledge discovered by reason.
7. In a world governed by reason, the true will always be the same as the good and the right (and the beautiful); there can be no conflict between what is true and what is right (etc.).
8. Science thus stands as the paradigm for any and all socially useful forms of knowledge. Science is neutral and objective; scientists, those who produce scientific knowledge through their unbiased rational capacities, must be free to follow the laws of reason, and not be motivated by other concerns (such as money or power).
9. Language, or the mode of expression used in producing and disseminating knowledge, must be rational also. To be rational, language must be transparent; it must function only to represent the real/perceivable world which the rational mind observes. There must be a firm and objective connection between the objects of perception and the words used to name them (between signifier and signified).