When What Is

[About this Article]

Today is Sunday.  Sunday is today.
Yesterday was Saturday.  Saturday was yesterday.
Tomorrow is Monday.  Monday is tomorrow.

This month is April.  April is this month.
Last month was March.  March was last month.
Next month is May.  May is next month.

This year is 2019.  2019 is this year.
Last year was 2018.  2018 was last year.
Next year is 2020.  2020 is next year.

This decade is the Teens.  The Teens is this decade.
Last decade was the Oughts.  The Oughts was last decade.
Next decade is the Twenties.  The Twenties is next decade.

This century is the 21st.  The 21st is this century.
Last century was the 20th.  The 20th was last century.
Next century is the 22nd.  The 22nd is next century.

Now are you clear about when what is?