On Second Thought

On second thought is what we we say when we want to change our opinion about a previous statement, meaning not trusting your first instinct. For example:  Why don't meet at the cinema? On second thought, I'll pick you up at your house.

On second thought, I don't want to talk about how we can't make up our minds [1]. Instead, I want to talk about how we confuse various words that sound similar to thought, such as though, thorough, through and throughout.

Though (zo) is a conjunction that we use to present a contrary idea. It has a similar meaning to but, however or despite.

That's a good answer, though not the correct one.

You can also add the prefix al- to mean the same thing.

Although I like Mexican food, I'd rather eat at a Thai restaurant.

Thought (zaut) is the past simple form of the verb think.

I thought you said we were going out tonight!

Youcan also add the suffixes -less or -ful to form adjectives.

thoughtless (not considering consequences)
How could you be so thoughtless and not call on my birthday?!

thoughtful (dareful consideration)

That was so thoughtful of you to send me flowers in the hospital!
You can even add -ly at the end of these adjectives to form the adverbs 
thoughtlessly or thoughfully

He looked thoughtlessly / thoughtfully at the mirror.
Or even add -ness at the end to form the nouns

thoughtlessness or thoughfulness

Your failure is a result of your total thoughtlessness.
A little thoughtfulness can go a long way.

Thorough (zo-ro) is an adjective that means the same as complete.

I want you to do a thorough cleaning job!

You can also add -ly at the end to make the adverb form.

She thoroughly enjoyed the birthday dinner!

You can even form compound nouns.

thoroughfare (a road or path that connects two places)
The street we live on is a busy thoroughfare.

thoroughbred (a pure breed [2])

They raise thoroughbred race horses.

Through (zru) is a preposition, which means from one side to another.

We walked through the park.

Don't confuse through with its homophone threw, which is the past simple form of the verb throw.
The pitcher threw the ball to the catcher.

Throughout (zru-out) is another preposition. It can mean...
from the beginning to the end of time:
The teams played intensely throughout the game

or all over a place:

Football is popular throughout the world.

Listen to the recording below.

[1] decidirse, [2] pura sangre