You seem to be making a lot of progress.
- (I am in the gym now and think about whether to call a friend.)
First, about the sentence above:
Usually with a sentence like this, you will see "... and am thinking about..." instead of think. There are some use cases for your formulation, though - think could be interpreted as present tense, which I think is your intent, but because you didn't use the expected "am thinking about", the listener could interpret it as an (awkward) imperative sense of think (but they will know that is not likely to be your intent.
Hopefully nobody edits your post and makes that part confusing. I understand that that is not the question you're asking, but it may be useful to someone if I point it out. Especially if they check out this excellent post on quora:
Quora, on "am thinking" and "think"
(1) Me: If I called him now, I would tell him that I am in the gym.
Is the am correct here?
- Yes, and I think there is only one way to interpret this sentence
(2) Me: If I were to be honest now, I would tell her that I ate her sandwiches yesterday.
Is the ate correct here?
- Yes, and again I don't see any other interpretations
Is ate simply in past tense because the action happened yesterday, right?
Yes, exactly. But I want to discuss the "would" part, after first pointing out a grammatical error:
- You might benefit from looking up what Wikipedia has called "declarative questions"
- If you change the first two words into "Ate is", you form a declarative question with good grammar.
- Alternately, remove the word "right" from the end of the sentence. Basically, you are sort of asking two questions in the same sentence.
note my edits in bold:
- *it is not being spelled like the past tense because of the conditional sentence, right? It really is in the past tense.
Correct. (Although technically we shouldn't say the word is in the past tense, in the first possibility. It is only spelled the same. There are several ways to fix that)
But you're right; "if" and "would" don't modify "ate". Your use of "Now" improves clarity. The "would" is referring to your intent - it isn't related to "ate" - it is about you, the speaker, being willing to tell her (something). But importantly, I have switched the order of "is it" to "it is" - again, this is a declarative question, making the "right?" part a mistake.
I'll make another declarative question that works the same:
- It isn't because it is being changed by a conditional, so that its spelling is that of the past tense, right?
tip: Starting with "Not" in the following is essentially adding on to the previous question:
Not because it is being changed by a conditional so that it is spelled the same way that the past tense is spelled?
There are many nouns and verbs there, but still this is not a complete sentence. It is all a big "because" clause, I guess you could say. So you should remove "right?" (Or stick "It is" at the front)
(3) If I told my friend that I am going to buy him a gift, I wouldn't surprise him tomorrow.
Is the am going to buy correct here?
Yes, this sentence is grammatically correct, but it might not be your intent.
The following sentence is the most likely intent:
- If I told my friend that I am going to buy him a gift, it wouldn't be a surprise.
Your construction follows all the rules, but "it will surprise (someone)" is generally more natural than "I will surprise (someone)(with something)", and avoids some unwanted meanings.
Note that the statement is a general truth about surprises - it is describing the nature of reality. Everybody knows that if you tell someone something is going to happen, it is no longer going to be a surprise. (To give a usage case, perhaps another friend has just asked you why you didn't tell your first friend that you were going to buy him a gift, and you are implying that you want to surprise him with it.)
It is a little tricky to know all of the uses of words like "would" But if you want to attack the problem, this Wikipedia entry on the irrealis mood might help a bit. Not everyone uses that term, but basically the irrealis mood is about things that aren't real; i.e. they haven't happened.
Hopefully this sprawling treatise will help someone. Gotta love procrastination :)