What is the difference between this and that?

The difference between these two words is subtle, which is why they can be difficult for non-native speakers.

​While this article is in the determiners section, both words are also pronouns. Since their usages are the same, this article will deal with both.
With objects (space)
A general rule is that 'this' is used with objects within reach and 'that' is used with objects out of reach.
For example:​
  • "This car is too old to drive" may be said while sitting inside the car.
  • "That bird looks like it is falling" may be said while watching a bird in the sky.​​
If there are two objects within reach, use 'this' for the closer one and 'that' for the further one.
​
With events (time)
A general rule is that 'this' is used with events that are contemporary and 'that' is used with events that are in the past or future.
For example:
  • "This is great" may be said while on a roller-coaster ride.
  • "That was awesome" may be said after a roller-coaster ride.
Please note that everything is relative to the point of reference. For example, 'that night' could be in the past but still in 'this year'.
​
In other cases
When using these words with nouns that are outside of the physical world or time, the difference is less easily articulated.

The best approach is to use 'this' when the ideas are continuous (not interrupted) and 'that' when the ideas are separated (but still related).

For example:
  • The government aimed to standardize education; this policy was laid out in bill 115.
  • Although the government enjoyed a majority in both houses, that bill never became law.
​In the first example, 'this' is used because it continues on from the idea it is referencing. In the second example, 'that' is used because a new idea is introduced which separates it from the idea it is referencing.

It is often the case that, if enough context is provided, these words can be substituted with 'the'. A good approach is to substitute when the noun has been previously mentioned.
Based on the above examples:
  • ​Since the word 'policy' has not been mentioned, use 'this'.
  • Since the word 'bill' has been mentioned, use 'the'.