How do you say "I think X is Y"


I've been thinking of this for a while and I need a bit of a clarification.
For example, if I want to say "I think he is a good person", would it be:

**a)** 私は彼がいい人と思う

or

**b)** 私は「彼はいい人」と思う

Also, if it has already been established from beforehand that I am the topic
of the sentence, would it then be possible to shorten this to 彼がいい人と思う or
彼はいい人と思う (whichever one is right from the first part)?




When you use a quotative-と, the "quote" will basically be a normal non-polite
sentence. That is, you can safely use は inside the quote, and you should not
drop だ. Brackets are usually not used in a simple case like this. Therefore,
the correct sentence is:

> 私は彼 **は** いい人 **だ** と思う。

The polite version is:

> 私は彼はいい人だと思います。

As you may already know, 私は is _normally_ omitted, so the following is almost
always more natural unless you have to emphasize "I":

> 彼はいい人だと思う。 / 彼はいい人だと思います。

Note that this does _not_ mean something like "He thinks (about) a good
person". See [this question](https://japanese.stackexchange.com/q/17984/5010)
for the reason.

* * *

There are exceptional cases regarding と:

  * だ is sometimes dropped in informal sentences (known as だ抜き). 私は彼はいい人と思う is acceptable in a casual conversation.
  * `A + を + B + と + verb` is a different construction from this, and you can safely drop だ in such cases. 

These are discussed in [this
question](https://japanese.stackexchange.com/q/55990/5010), but if you are a
beginner, you may want to learn about them later.




When you use a quotative-と, the "quote" will basically be a normal non-polite
sentence. That is, you can safely use は inside the quote, and you should not
drop だ. Brackets are usually not used in a simple case like this. Therefore,
the correct sentence is:

> 私は彼 **は** いい人 **だ** と思う。

The polite version is:

> 私は彼はいい人だと思います。

As you may already know, 私は is _normally_ omitted, so the following is almost
always more natural unless you have to emphasize "I":

> 彼はいい人だと思う。 / 彼はいい人だと思います。

Note that this does _not_ mean something like "He thinks (about) a good
person". See [this question](https://japanese.stackexchange.com/q/17984/5010)
for the reason.

* * *

There are exceptional cases regarding と:

  * だ is sometimes dropped in informal sentences (known as だ抜き). 私は彼はいい人と思う is acceptable in a casual conversation.
  * `A + を + B + と + verb` is a different construction from this, and you can safely drop だ in such cases. 

These are discussed in [this
question](https://japanese.stackexchange.com/q/55990/5010), but if you are a
beginner, you may want to learn about them later.

