Basic Modals

https://englishlessons140.files.wordpress.com/2015/04/topic-8.pdf

Modals are used to moderate the main verb.
Some common modals: can, could, may, should

Can / Can't

showing ability/inability or possibility/impossibility　
　　　　　（能力/不能または可能性/不可能性を示します）
  (I can pay my taxes.; She can't dance.)


Could

requesting　（要求）
   (Could you pass the sauce please?)

giving suggestions　(提案を与える）
   (We could try doing the homework like this.)

future possibilities　(今後の可能性）
   (I think I could go to the concert next week.)

past abilities　(過去の能力）
(She gave up her job so she could take care of her children.)


May

asking for permission　(許可を求める）
  (May I have another cup of coffee?)

future possibilities　（今後の可能性）
  (You may apply for this school.)


Should

saying what's right or correct / recommending action　（すべき・推奨）
　(We should solve this as soon as possible.)

uncertain guess　（不確かな推測）
　　(Business should be good this year.)