The preconditions for a (pre-)revolutionary situation?

I've heard them before. During meetings of the CWI there was sometimes mentioning of Trotsky and Lenin who supposedly wrote about the preconditions for a revolutionary or prerevolutionary situation. Does anyone know where I can find them?

There's a difference between objective and subjective prerequisites for revolution.

Here are some works dealing with the subject by Lenin and Trotsky:

Trotsky:

The Pre-Requisites of Socialism
The Objective Prerequisites for a Socialist Revolution
The Pre-Requisites of Socialism

Lenin:

On Cooperation

There aren't a lot of works by Lenin dealing with this issue specifically, but he refers to it quite often in his other works. For example, in his theses for The Socialist Revolution and the Right of Nations to Self-Determination he writes this about the possible subjective prerequisites for revolution:

The socialist revolution may break out not only in consequence of a great strike, a street demonstration, a hunger riot, a mutiny in the forces, or a colonial rebellion, but also in consequence of any political crisis, like the Dreyfus affair, the Zabern incident, or in connection with a referendum on the secession of an oppressed nation, etc.

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