Ditto G-Cam, but let me add an additional comment.
As G-Cam says, "only the X", means that there are several things under discussion, but right now the one we are interested in is the X.
"The only X" says that there is only one thing that qualifies as X.
In your example, talking about the "second square", the second usage doesn't make much sense. Presumably there is only one square that is "second". I wouldn't suppose there could be 5 or 10 "second squares".
But suppose I said something about the "red square". If I said, "Consider the only red square", that would mean that while there may be many squares, only one of them is red. I am emphasizing that there is only one red square.
"Consider only the red square" says that I am calling your attention to the square that is red. The fact that I use the singular "square" implies that there is only one, but the sentence structure is not emphasizing that there is only one, but rather assumes this, and then emphasizes that this is the one we are interested in.
But it's perfectly possible to say *It is only the car we have* (we don't have anything except the car) or *It is the car only we have* (no-one except us has this car). The thing is we normally try to position *only* immediately before the specific element it's intended to modify. In your example, that's just *car*, not *the car*. – FumbleFingers Reinstate Monica – 2016-09-07T15:00:11.130
@FumbleFingers your "only we" example is not germane to the original question as it has nothing to do with the placement of only relative to a determiner. Why not put up your own answer: "put only immediately before the element it is intended to modify"? – Tᴚoɯɐuo – 2016-09-07T16:33:41.607
How do we know what's "not germane to the original question"? You've assumed it's obvious to everyone that OP is only concerned with contexts involving [determiner] only [noun], and that the first line of your answer should therefore be understood to be relevant to that context only. Looking again at the way you've presented things I see the first line isn't in fact a "general prescription". But that's what it looked like to me when I first read it. That's to say if I'd put my reading glasses on I wouldn't have been surprised to see a full stop after *...and noun.* – FumbleFingers Reinstate Monica – 2016-09-07T16:49:12.673
I refer you to the title of the question. – Tᴚoɯɐuo – 2016-09-07T16:51:31.723
I don't know why two clever guys like us are arguing over this minor point. If you'd put your When the meaning is... clause *before* the initial assertion I wouldn't have misparsed it as a general rule rather than being restricted to one specific context. In which case I wouldn't have felt moved to point out that there are other contexts where it doesn't apply. Okay, you may say I'm not in fact smart, and/or that I should pay more attention to your text. But I'm a competent native speaker, and if it caught me out it might well mislead some of our target audience here. – FumbleFingers Reinstate Monica – 2016-09-07T17:12:35.773
You been ended up typing too soon. – Tᴚoɯɐuo – 2016-09-07T17:17:48.100
Arguably I've been upended. From OED: *To force back the end of (a metal bar, etc.) by hammering or beating, esp. when heated.* Are we getting heated here? Am I being forced back? (I hope not to both! :)
– FumbleFingers Reinstate Monica – 2016-09-07T17:34:20.903