In general when we look at an English sentence to see who is doing what to whom (grammatically speaking), we can say that the subject does something to the object:

{subject} + does something to + {object}

Jesse Owens + won + 4 gold medals.

I + believe + your sister.

The objects in these two examples above are two noun phrases‏‎: 4 gold medals and your sister.

However, we can also use a complete clause as the object of a sentence (a clause contains a verb and a noun). Here is a simple clause:

You are wrong.

When we use this as an object in a sentence, it becomes an object clause:

{subject} + {verb} + {object clause}

I + believe + you are wrong.

Examples of Object Clauses

Each of the following sentences has its object clause highlighted:

I know he is lying.

We didn’t realize she was so ill.

The company has admitted to supplying the tax authorities with false information.

Object Clauses and Passive Voice

Here is a sentence which has an object clause:

{subject} + {verb} + [that] + {object clause}

People + say + that + Jesse Owens was one of the most important athletes of the 20th Century.

To make this passive we use what is known as the impersonal passive form:

{it} + {passive verb} + [that] + {object clause}

It + is said + that + Jesse Owens was one of the most important athletes of the 20th Century.

If the verb in the object clause is in the present simple‏‎ or past simple‏‎ we can build the passive sentence in yet another way.

{object} + {passive verb} + {passive infinitive}

Jesse Owens + is said to be + one of the most important athletes of the 20th Century.

This happens when you talk about an opinion, suggestion or belief which uses a verb like: believe, claim, estimate, say, think and so on.

We often use these patterns with reporting verbs such as: agree, arrange, announce, believe, consider, decide, expect, fear, feel, find, hope, intend, know, mention, regret, report, say, suppose, think, understand.

Useful Links

Sentences in English – a general look at making sentences in English

Subjects and Objects in English grammar

Passive Voice‏‎ in English – for more on the passive voice