Could there be a more innocuous word in the English language than and ? Said so often every day, we sometimes barely even pronounce it, but still it remains the force it is to connect and hold parts of our sentences together. Without it, our words would spill out like beads off a string, pieces of thoughts everywhere and meaning difficult to discern.
The grammarians classify and as a conjunction, a word or phrase that connects sentence elements into a meaningful statement. We can see the word junction in the term, a point of meeting, and it can help to picture this idea to see just where—and how—conjunctions bring elements together. In the sentence It began to rain and Tom left, the conjunction and represents that point where two independent clauses meet. Traditional grammar goes one step further in the classification and calls and (and others like it) a cumulative conjunction because at that point, the sentence continues on by simple addition, a second independent clause (Tom left) being joined to the first (It began to rain) in order simply to present two ideas in a general association. The result is a compound sentence.
But here is where the innocent and can turn hazardous if we rely on it to do more in joining clauses than it is designed for. There are two great classes of conjunctions, coordinating and subordinating, and each has a number of sub-categories. Under the coordinating heading, there are cumulative conjunctions, like and, that associate things; adversative conjunctions, like but and however, that dissociate things; and illative conjunctions, like therefore and so, that present a conclusion or result. Under the subordinating heading, there are causal conjunctions, like because and since, that show reason or cause; conditional conjunctions, like if and unless, that indicate a supposition of some sort; and temporal conjunctions, like when and after, that stipulate time. We might like to resist all the minutiae that classification lays bare (and grammar is rife with classification!), but the theory of grammar follows its practice: apparently that’s just how complex our thinking is.
So what does it really mean to say, It began to rain and Tom left ? If we take and at face value, then the sentence is doing nothing more than delivering two thoughts in one package: we open the box (the compound sentence) and find two items (the two independent clauses) separately wrapped but sent together. The fact that they arrived in one box surely implies that they have something to do with each other, but there’s no note to say just what. And that’s the problem with and: it won’t take a stand. If we look down the scale of conjunctions and choose so, we produce one thought: It began to rain, so Tom left. Now we’ve found some instructions in the box, and know that Tom’s leaving was the result of its beginning to rain. And the instructions will be different again if we change and to after: It began to rain after Tom left says nothing about the reason for Tom’s leaving, but only asserts what happened subsequent to it. Not every conjunction can substitute for any other, of course, because the laws of logic and reality hold sway (what would it mean, for example, to say, It began to rain if Tom left ?), but choosing the conjunction that best represents the logic of our thinking is one important way we can write more clearly.
And therein lies the danger of and. By nature genial and generous, it accepts all comers and doesn’t ask too many questions. The cumulative conjunction and in It began to rain and Tom left can imply any logical connection that’s possible between the two ideas. Did Tom leave because it began to rain? Did Tom leave as a consequence of its beginning to rain? Was the fact that it began to rain the reason Tom left, or was it just a coincidence that it began to rain when Tom left? And includes all of these ideas, which is the reason it is important to look closely at it when joining clauses: another conjunction may express the thought more exactly—and that is always the direction we want to take.