Form : ( Was / were supposed to + infinitive (verb 3) )

In English we use was / were supposed to to talk about things we agreed to do, or other people expected us to do, but we didn't do.

Example sentences :

• I was supposed to book the restaurant for tonight, but I forgot. ( I agreed to do it, but I forgot)
• David was supposed to take the boys to football training tonight, but he had to work late. ( David was expected to take them, but he couldn't)
• Jenny was supposed to water the plants while I was away. but she forgot.
• Tony was supposed to cook dinner tonight, but he had to work late.
•  Fiona was supposed to organise a conference call for this morning, but she couldn't get in touch with her colleagues.

Notes for use of was / were supposed to : 

In English we often use this form to apologize for not doing something and give a reason why.

• Sorry, I was supposed to buy some bread on the way home, but the bakery had closed.