# Gumshoe: the investigative to general ability exchange rate

In the previous (and first) installment of this series I looked at what I think of as the *kernel* of Gumshoe’s system. In this short post, I want to have examine the relationship between the investigative abilities and the general abilities.

There are places in Gumshoe allow the (limited) exchange rate for investigative abilities to general abilities. The most common instance is a special benefit where an investigative spend generates a dedicated pool and wants to spend some of that pool as on a general ability. Without other qualifiers that number is 1:3^{1}. Where does this number come from?

Where it comes from is actually a fairly simple question: let’s look at what it takes to guarantee success with each subsystem, with the kernel in mind. Recall that the default general ability test is 50/50, or a difficulty number of 4 on a six sided die. Therefore to guarantee success you would need to spend 3 points.

Investigative abilities don’t test in the same way, but if you consider the simplest case of a benefit, a one point spend, then it’s simple to see that you succeed 100% of the time by spending a single point and ‘fail’ 100% if you don’t.

Therefore 3 general points are conceptually equivalent to one investigative point (or a push). So with no other considerations in play, that’s our baseline.

What other considerations should be in play? Well, the obvious one is that when spending an investigative point, imagine it was a test of a general ability, and your sense of the story pacing would increase the difficulty number, then the resulting pool would need to be smaller. This is to compensate for the chance of failure the higher difficulty now represents.

Why might you want to use investigative pools as on general tests in play? Think of it as a extension of the recommendation that a benefit “…can also provide information that is usefully applied to later contests involving General abilities” (Trail of Cthulhu, pg 54), but applied to *Dedicated Pool Points* rather than to just narrative positioning.

For example: A player might get special benefit from a 1 point *architecture* by looking up plans for the building being used as a cult temple that is a dedicated pool of 2 *Cult Temple Buildings*. Later, the investigators are trying to cut power to parts of the building with *Electrical Repair*, and they want to spend one of the *Cult Temple Builds* points on it. Easy: just give them a 3 point bonus to the roll, leaving them one point in the dedicated pool. Maybe they’ll spend that on an other investigative test, or perhaps they will need to make a piggybacked *flee*, and they'll will use the 3 points to make up for the investigators who can’t afford the tax.

Next time, what constitutes competency for Gumshoe characters.

- The actual value is rarely denoted in the game texts. For an example, Trail of Cthulhu, page 25, Trading Points offers this specific exchange at character creation time.
- Or possibly I’m just terrible at trying to find examples in the rules text.