The document discusses the conditional mood in simple sentences. The conditional mood is formed using "should/would + the infinitive" and can be perfect or non-perfect. It represents an action that contradicts reality. The conditional mood is used with an adverbial modifier expressing condition, with an implied condition, or to sound polite. It discusses the different forms like "should/would have done" and how "should" and "would" can both be used for the first person in modern English.