Q:

Meaning of the word can in this sentence

I am reading Clarissa by Samuel Richardson and I am not sure that I have understood a sentence correctly. Thank you very much in advance for your help.
Lovelace tells Clarissa that in the midst of his mild vagaries he has ever preserved a reverence for religion, and for religious men and that the good men of the clergy call him a decent rake and he goes on by saying:

"This madam, I am the readier to confess, as it may give you hope that the generous task of my reformation, which I flatter myself you will have the goodness to undertake, will not be so difficult a one as you may have imagined; for it has afforded me some pleasure in my retired hours, when a temporary remorse has struck me for anything I have done amiss, that I should one day take delight in another course of life: for without one can, I dare say no durable good is to be expected from the endeavour.

The word "can" seems to me to be used as a noun. I have looked all its accepted meanings up but to be honest none convinced me. From what Clarissa says afterwards I understand that it can mean "delight". She says: 

"I told him that his observation that no durable good was to be expected from any new course where there was not a delight taken in it, was just: but that the delight would follow by use.

A:

This is a novel from the 18th century. English usage has shifted somewhat since then. Vocabulary has changed; words have fallen out of use, or come into use, or shifted their meaning. Even the sort of grammar used has changed in places. So, you have to expect reading such a work that you will run into things that will baffle even the typical modern native speaker.
In this case, "for without one can" would be likely to be phrased, nowadays, as "for unless one can". In more everyday speech, in that context, we might say "unless you can do that", using the general you rather than one, and making the argument of can explicit - and dropping the largely redundant for. What she is referring to, the thing that one must be able to do in order to "expect durable good from the endeavour", would appear to be "one day take delight in another course of life".

