What is the difference between these two sentences?

  1. I thought you would know
  2. I thought you knew

These two sentences look the same to me. In which situations do you use each variant?

  • 2
    'I thought you knew' means 'I [wrongly] was convinced that you possessed this information [and I must have been mistaken]. // 'I thought you would know' means 'Though I wasn't certain, I thought it highly likely that you would possess this information'. Jun 18, 2018 at 9:50

2 Answers 2


I'm surprised this has been migrated over from the Big People site. I'm a native speaker and I'm having trouble figuring it out. All I can offer is an example showing where I'd tend to use each. But I may be wrong!

Alan is asking his friend Bob for some advice on taking Claire out on a third date:

Alan: So, big night tonight; third date! But I'm fed up going to vegetarian places for Claire. Do you think Outback Steakhouse will have something suitable for her, so I can have some cow?

Bob: What!? You're dating her now? I knew you fancied her but ... when did that happen?

Alan: About a month ago. I thought you knew.

Bob: Nope. No one tells me anything.

Alan: But the restaurant ... steak for me, and veggie stuff for her; what do you think?

Bob: Ermm, I guess. I mean suppose it... I dunno! What are you asking me for?

Alan: Well I thought you would know. Aren't you vegetarian?

Bob: No, I was vegetarian. But I gave it up last month. I missed bacon too much. I thought you knew that!?

Alan: [grins] Nah, I've been too busy fantasizing about Claire. I'd have thought you'd have known that.

Just threw in that last form to make things even more complicated :-)


"I thought you knew" indicates that you thought they were aware of it in the past, typically of something you just informed the person of. (Because obviously they know it now. You just mentioned it, so you say this phrase to indicate why you hadn't said so earlier.) "My dog died last week. I thought you knew."

"I thought you would know" is used when you were looking for information from that person. You thought they would know, but now you know for sure if they do or not. "I have no idea." "Oh, I thought you would know."

It can also be used to indicate a conclusion you would assume they would have drawn or something they would have picked up on, but apparently did not. "Given how much I'm on campus, I thought you would know that I'm a student."

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