Do not put statements in the negative form.

This is William Safire’s third rule of grammar. Two more to go.

Here’s the late, great Ella, telling us about it. 

Using the advice, the title, above, would be: Put statements in the positive form.

Right? Okay, but don’t we have to use negative statements sometimes? I honestly don’t know what this one is about.

But I did some research on negation and found some esoteric things.

Like, the subtle difference between these two statements:

      (1) I don't think [that he came] (I don't know what he did)
          (2) I think [that he didn't come] (I think that he stayed away)

And these not-so-subtly different statements:

      (1) I didn't say [that he lied] (I said nothing)
          (2) I said [that he didn't lie] (I said that he told the truth)

The above are taken from:

https://www.thoughtco.com/negation-in-grammar-1691424

Any more thoughts on this?