怎么样理解主句的虚拟语气形式？

Over the green squares of the fields and the low curve of a wood there rose in the distance a gray, melancholy hill, with a strange jagged summit, dim and vague in the distance, like some fantastic landscape in a dream. Baskerville sat for a long time his eyes fixed upon it, and I read upon his eager face how much it meant to him, this first sight of that strange spot where the men of his blood had held sway so long and left their mark so deep. There he sat, with his tweed suit and his American accent, in the corner of a prosaic railway-carriage, and yet as I looked at his dark and expressive face I felt more than ever how true a descendant he was of that long line of high-blooded, fiery, and masterful men. There were pride, valour, and strength in his thick brows, his sensitive nostrils, and his large hazel eyes. If on that forbidding moor a difficult and dangerous quest should lie before us, this was at least a comrade for whom one might venture to take a risk with the certainty that he would bravely share it.



上段节选中，最后If on that forbidding moor a difficult and dangerous quest should lie before us, this was at least a comrade for whom one might venture to take a risk with the certainty that he would bravely share it. 该句中:



If...shoud lie..., this was...是虚拟语气吗？ 是对以后的虚拟假设，if从句用should lie, 表明可能性极小，

但主句是不是用了would/should/could/might+do呢？

主句中的this was - was 该怎么样理解？ 也是虚拟吗？如何理解呢？为何不是were?



请老师剖析主句的虚拟形式。



If on that forbidding moor a difficult and dangerous quest should lie before us, this was at least a comrade for whom one might venture to take a risk with the certainty that he would bravely share it.

if从句用should do形式，主句可以用虚拟语气、陈述语气或祈使语气。本句中主句谓语动词用was, 即主句用了陈述语气，说明if从句为真实条件句，即从句的条件有达成的可能。

真实条件句中，主句可以不需要情态动词。比如：

If you make one more mistake, you are fired.

你的句子就是类似使用方法，只是说话人的立场不是目前，而是过去，所以主句用was表示过去以后的时间。

另外，虚拟语气形式were只用于从句，不会用于主句的。