Adding Candy Sugar

Will adding 1/2 pound of Belgian Candy Sugar to a 5 gallon batch towards the end of primary fermentation take the finishing gravity lower than without the addition? It is the Saison I Ale (WLP565) yeast.

No. If anything it will raise the FG if there are any unfermentable sugars in it. It can be used to lower your FG if you replace some of your malt with the candy sugar in your recipe as it is much more fermentable than malt.

GT

Thanks a bunch

Assuming one intends to add the sugar regardless, would it tend to impact the FG either way? That is, would adding the sugar in the boil versus adding the sugar at the tail end of the primary make a difference?

My inclination is to say that adding the sugar towards the end of the primary would tend to give a lower FG, as the more easily fermentable sugars are added only after the less easily fermentables are "eaten," but I don't really have any experience either way.

Completely fermentable sugar will lower the FG, as EtOH has a lower specific gravity than water; this why a table wine with a 1.090 SG has a FG usually around 0.990. It won't matter when you add the simple sugar, the sugars will get used eventually anyway.
Assuming a mostly malt wort, so there's plenty of FAN, vitamins, etc, what matters is will the amount of potential alcohol exceed what will kill your yeast (varies by strain) and does yeast make an enzyme that can eat that sugar. Since Belgian candy sugar is sucrose already broken down into glucose (aka dextrose) and fructose, the answer to that is "yes".

This is why lactose can add body; Saccharomyces cerviseae yeast don't digest it.