The following is an example from Swan's Practical English Usage (515.2)

You won't be here tomorrow?

I don't suppose so.

I understand the answer "I don't suppose so" is the same as

I don't suppose I will be here tomorrow.

If the answer is "I suppose so", is it the same as the following?

I suppose I will be here tomorrow.


You are correct in your understanding of the usage as discussed in your grammar book.

You won't be here tomorrow?

I don't suppose so.

is a typical exchange, and the response means, "I don't suppose I will be here tomorrow."

A normal person typically answers an informal negative question by responding to what he thinks the asker really wanted to know. Strict rules of formal logic do not apply here.

If the conversation were:

You won't be here tomorrow?

I suppose so.

that would be confusing. If it was important, most people would ask a follow up question to clarify:

You mean you will be here? Or, you won't be here?

... Please note that the above is for US English. (I have no knowledge of other varieties.)


When you say, you don't suppose so, you are contradicting( asserting the opposite of what is said) the previous statement. Simple put, you beg to differ.i.e.

  • I don't suppose that I won't be there the following day. (You would be very much there.)

If you answer, " I suppose so.", you are endorsing his view point . So you are flawed in your understanding the tags.

  • (–1) This is wrong. Perhaps in your mother tongue things work that way, but that's not the case in English. As user Lorel C. explained, the first is used in agreement, and stands for "I don't suppose I will be here...", while the second version would be unidiomatic in such an exchange. – userr2684291 Jan 3 '19 at 12:57

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