I would like to hear some opinions from the grammar gurus here about the seemingly-extraneous use of "that" in modern English. Consider: "I know that the store closes soon." "I know the store closes soon." Both sentences seem perfectly grammatical to me, and I don't think either would raise any eyebrows. They convey exactly the same information. So what's up with that? Was it originally one way or the other? Is one of those example sentences grammatically incorrect for some reason that eludes me?
"That" is a conjunction in addition to its other roles. One of its uses is as a subordinating conjunction, connecting a primary clause to a subordinate clause: I told him -- that -- (subordinate clause) I was no longer interested in the position. That -- (subordinate clause) your CDs will get wet -- is the least of your worries if you car falls into the river. Where is the evidence -- that -- (subordinate clause) my client took merchandise without paying for it? Mary is disappointed -- that -- (subordinate clause) only ten people showed up at her birthday party. In some of these cases, eliminating "that" leaves the meaning of the sentence clear, but in others it either makes you stop and sort it out, or muddles it completely. In spoken vernacular English it's acceptable to leave out "that" in a sentence like your example. Verbs like know, think, say, hear, hope, write and believe guide us into expecting a subordinate clause to immediately follow. But we should always err on the side of caution. If there's the slightest doubt that omitting it will confuse the listener, then leave it in. And in any writing except the most casual, it's best to maintain a slightly higher level of formality than in speech, because so much of our communication bandwidth is carried by cadence, tone of voice, etc. She said she hoped I wouldn't think she forgot my wife is in the hospital. That sounds okay if you read it out loud but it's a little awkward in print.
