Learn English – what I should vs. which I should

• That's the shop which sells elephants.
• This is an elephant which the shop sold ____ .

In these sentences, the relative clauses have been marked out in bold. Each relative clause is like a small sentence inside the bigger sentence. In these relative clauses, I used the pronoun which. I could use the pronoun that instead. They are both okay for this kind of sentence, where the relative clause is restrictive.

1. which sells elephants.

2. which the shop sold ________ .

In clause (1), which is the subject of the verb sells. In (2), which is the object. It has moved from that gap at the end. We can see that which is behaving like a Noun in these sentences. This is because which is a Noun! It's a special kind of Noun, a Pronoun. Whenever we need to replace a noun inside a relative clause we use which or that - or who if it is a person.

Now let's have a look at a different sentence:

• I play football in the park.

We can divide that sentence into different sections. The Subject is I. The Predicator (the verb) is play and the Object is football. But what about that funny bit at the end, in the park? What's that?

In the park here is an ADJUNCT. Adjuncts like this that get put at the end of sentences usually begin with a Preposition like in, on or at, for example. Adjuncts can also sometimes be Noun Phrases or Adverbs:

• I play football every day.
• I play football daily.

But most often Adjuncts like this begin with a preposition. Adjuncts usually tell us information about why, when, how, who with or where something happened. That kind of thing. This information is always extra information. It isn't part of the essential grammar of the sentence. I play football still makes sense without an adjunct at the end.

The relative word where doesn't usually replace a noun! It replaces an adjunct or a preposition phrase - ones that tell us about where. (Remember that an adjunct will normally include a preposition and a noun). This also means it can't replace the Subject or Direct Object of a verb. It also can't usually replace a noun which is the object of a preposition (although remember that preposition phrases can also be the complements of prepositions). Where nearly always replaces a preposition phrase or an adjunct.

In the original Poster's sentence

• London Bridge is one of the most popular places wwww people want to visit ____.

We can see that that gap at the end there with the missing bit, is the Direct Object of the verb visit. We don't expect to see a preposition after visit either. This word can't be an adjunct or a preposition phrase. It looks like it must be a Noun Phrase. Therefore, we need to use which or that. A good rule-of-thumb test to see if it should be which or where is to see if you could put the word it or them in the gap. If you can, you can use which:

• London Bridge is one of the most popular places which /people want to visit it/.

If you can't but you could put the word there in the gap, then you should use where:

• ... the house where /I used to live there/

Edit note

For some speakers, this rule -that where can't replace direct objects doesn't seem to be so strict. See F.E.'s comment about his variety of English. For my dialect - I'm a British English speaker - this rule is quite strict.

Hope this helps!

You don't need to capitalize the o in the word "one" if it is not the first word of a sentence. The tutorial you watched is correct. The reason the first sentence is ungrammatical is because it is a run-on sentence, which is a very common grammar error. A run-on sentence has two or more parts (clauses), each of which can be a stand-alone sentence. (See how my sentence is similar to the sentences are you asking about?) To avoid making run-on sentences, you need to connect these clauses with conjunctions, such as "and", "or", "but".

So the problem with the first sentence is that "them" is not a relative pronoun and the clause is an independent clause. You need a conjunction to connect the two clauses if you want them both in one sentence.

I have two assignments, and one of them is done.

Or alternatively you need to make them two separate sentences, which means you need to replace the comma with a period.

I have two assignments. One of them is done.

The second sentence reads fine as long as you follow the correct sentence case and change "One" to "one".

I have two assignments, one of which is done.