It’s good to be precise. But when the future is sufficiently uncertain that you can’t be precise, vagueness comes in handy.
But there’s vague and there’s vague.
Consider reasonable. Because reasonableness isn’t determined by objective criteria, determining whether a given act is reasonable requires (1) a potentially messy inquiry into the surrounding circumstances and (2) measuring the findings against one’s notions of reasonableness. So determining reasonableness is an exercise in line-drawing, and there’s no guarantee that you and I are going to come to the same conclusion regarding whether a given act was reasonable.
But at least anyone trying to determine whether something was reasonable has a decent idea of what the standard is, even if applying it is fraught with uncertainty. By contrast, consider substantial and substantially. Here are some examples from EDGAR:
Effective as of the Separation Date, AANI agrees, and agrees to cause the other members of the AANI Group, … to take such actions as may be reasonably requested by AgFeed to enable members of the AgFeed Group to receive substantially the same rights and benefits under a Shared Contract received by members of the AANI Group.
If Holdings declines (or is deemed to decline) such Offer, the Seller shall have the right to effect a disposition of the Offer Interests on substantially the same or more favorable (as to the Seller) terms and conditions as were set forth in the Offer Notice at a price not less than the Offer Price.
[N]one of the officers or directors of the Company is presently a party to any material transaction with the Company … , including any contract, agreement or other arrangement … requiring payments to or from any officer or director or, to the knowledge of the Company, any corporation, partnership, trust or other entity in which any officer or director has a substantial interest or is an officer, director, trustee or partner.
Substantial and substantially exhibit the same problem as aggressively, which I ranted about in this October 2010 AdamsDrafting blog post. How big does something have to be before it is substantial or can be said to do something substantially? More than 50% of its maximum potential magnitude? More than 70%? 85.42%? I have no idea. So the subjectivity inherent in vagueness is compounded by imprecision.
Maybe substantial and substantially refer to a magnitude that’s close enough to the maximum that a reasonable person in the position of whoever has the benefit would be satisfied. That may be the case, but I’m not aware that that meaning is sufficiently accepted that you can take it for granted.
Perhaps material or materially would be a better bet to articulate that meaning, as long as you make it clear that you mean the more exacting of the two possible meanings of material—something is material if it would affect a person’s decision-making. See MSCD chapter 8 or this February 2007 AdamsDrafting blog post. At least material is vague in the same way that reasonable is vague.
I’ve never found a satisfactory test. I have wrangled with the substantial evidence (“real”, “palpable”) test in appeal and the concept of substantial completion in construction contracts. In the latter, it generally indicates nontrivial matters may remain incomplete but that the building or whatever can be used for its intended purpose. If you’re are dealing in an area where there isn’t at least significant/substantial amount of decisional law, it may well be better to get more specific.