1. I had a book.
2. I'd a book.
3. You had a pen.
4. You'd a pen.
5. He had a car.
6. He'd a car.
7. We had many pens.
8. We'd many pens.
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Are the contracted forms all grammatical?
Nope. None of them are.
For these contraction forms to be correct, you need to use them only when "had" is an auxiliary or helping verb.
I had a book. ("had" is the main verb and is not to be contracted)
I'd been staying at her house until I found my own place. ("had" is an auxiliary verb with "been" and thus can be used in contracted form)
Yes, the contracted forms in sentences 2, 4, 6, and 8 are all grammatically correct. These contractions involve combining the subject (I, you, he, we) and the auxiliary verb (had) using an apostrophe to form the contracted version (I'd, you'd, he'd, we'd).
The contracted forms are common in spoken and informal writing. They are used to create a more casual tone and to save syllables when speaking or writing quickly. However, it's important to note that contractions are generally not used in formal writing, such as academic papers or formal letters.