I leaped over three "treads" or "stairs" while climbing stairs.

First, the simple past and the past participle of "leap" is leapt, not "leaped." Tread might be more commonly used in British usage rather than American usage. Whether you aspire to learn British usage or American usage will determine what noun you use. In American usage, one would say "step."

So one would say: "I leapt over three steps while climbing the stairs." One would use the definite article, "the," when referring to the noun stairs--at any event, that would be common American usage. It might be different in British usage, I am not qualified to say. Furthermore, in common American usage, one would say: "I leapt up three steps at a time (or, at once) while climbing the stairs." For descending the stairs, in common American usage, one would probably say: "I leapt down three steps . . . etc."

I would say that what Setanta says about American usage applies equally to British English. We climb the stairs when talking about specific stairs but a disability or injury might prevent one from climbing stairs in general. Also, hardly anyone talks about 'treads' and/or 'risers' except people discussing technical details of staircases, for example carpenters, builders, carpet fitters, etc. As for leaped and leapt, I think leaped was more common in all varieties of English until about a century ago, when leapt became more common in British English. Today, both forms are frequently used in American and Canadian publications, while publications from outside North America tend to favour leapt. This is interesting, because other past-tense forms ending in '-t' tend to have fallen out of use or become decidedly minority in AmE from around 1850-1900, while being interchangeable with their '-ed' counteparts elsewhere - spelled/spelt, burned/burnt, learned/learnt, etc. According to this Ngram, spelt is losing ground to spelled in BrE:



I am intrigued by the Google Ngram Viewer, and plan to play around with it if I can find some instructions.

1. Leaped vs. leapt (British English)



2. Leaped vs. leapt (American English)

As an American, I use leaped and the few times I have come across leapt in literature I just assumed it was a British usage.

Damn-charts for language usage. I never expected that. I like it-using the tools of science and engineering on cultural phenomena. Should yield a lot of knowledge, (and settle a lot of arguments).

I tried the Ngram Viewer on a number of words, including lesbian, ****, homosexual, and they all cling to the bottom of the graph until about 1960 and then ascend like skyrockets.

On the other hand, here is the N-Word in American English between 1820 and 2000



Here's the Ngram Viewer, it's pretty simple to use.

https://books.google.com/ngrams

When he was climbing stairs while being chased he kept leaping up two or three stairs to reach at the top as quickly as possible.

He keeps leaping down stairs while descending stairs.

Are my sentences correct?

No, they are not. Stairs refers to the entire construction. Each part of the construction should be referred to as a step.

Do you really expect anyone to believe that you (or anyone else) can run upstairs three steps at a time? That's silly--two steps is enough of an effort. Running downstairs, no matter how many steps you leapt would make you an accident waiting to happen. Trip while you're running upstairs, and you'll at least crack you head on the steps. Trip while you're running downstairs, and you'd be lucky if you didn't kill yourself.

The use of language needs to make sense, too.

When he was climbing stairs while being chased he kept leaping up two steps to reach at the top as quickly as possible.

He keeps leaping down steps while descending stairs.

Are these correct?

I don't think you really pay attention to what you are told here. You need to use "the stairs." Those two sentences are technically correct, and they have the virtue that no one will mistake you for a native speaker .

When he was climbing the stairs while being chased he kept leaping up two steps to reach at the top as quickly as possible.

He keeps leaping down steps while descending the stairs.

Are these sentences correct now?

"they have the virtue that no one will mistake you for a native speaker" what does it mean I don't understand? Could you please explain?