-ward(s)
Backward(s), forward(s), northward(s), outward(s) and similar words can be used as adjectives or adverbs.
Adjectives
When they are used as adjectives, they do not have -s.
- This country is very backward in some ways.
- You’re not allowed to make a forward pass in rugby.
- He was last seen driving in a northward direction.
Adverbs
When these words are adverbs, they can generally be used with or without -s. The forms with -s are generally a little more common in British English, and the forms without -s in American English.
- Why are you moving backward(s) and forward(s)?
- If we keep going upward(s), we must get to the top.
- Let’s start driving homeward(s).
In some figurative expressions such as look forward to, bring forward, put forward, the form without -s is always used.
- I look forward to hearing from you.
- She put forward a very interesting suggestion.
Other words
Towards and afterwards are the usual forms in British English; in American English, toward and afterward are also common.