What's the difference between 'allow' and 'allow for'?

To be precise, I know that allow means to permit, and allow for is more like to make something possible, to enable, to make a provision for, but I'm still in doubt when I have to decide whether to use the preposition for or not.

For example, in the sentence taken from Google Dictionary entry used to explain usage of allow:

They agreed to a ceasefire to allow talks with the government.

I'm not sure what I would use in this example — maybe even allow for.

I agree with Robusto, I think. There is a semantic difference between "allow" and "allow for". "B did X, allowing Y" implies that by doing X, B directly caused Y to happen. However, "B did X, allowing for Y" implies that doing X may or may not, in fact, actually cause Y; Y may happen with or without X, or Y may require something else to happen besides or in addition to X.

Short non-sequitur, but consider a sentence in the context of carpentry. "He spaced the boards a quarter-inch from the wall, allowing expansion". Those who know carpentry know that you don't "allow" boards to expand; they simply swell and shrink with temperature and humidity regardless of what you do. Instead, you must "allow for" the boards to expand by taking an action ensuring that WHEN they expand, there is no adverse consequence. So, the correct statement, in context, is "He spaced the boards a quarter-inch from the wall, allowing for expansion".

Back to your OP, "a ceasefire allowing talks" implies that talks will not happen without a ceasefire happening first. "A ceasefire allowing for talks" may imply that talks are already happening, or that they could happen regardless of a ceasefire, but that the ceasefire facilitates those talks. Either may be correct, depending on the situation being described.

So, "allow" denotes permission, and thus a direct cause/effect. "Allow for" denotes either facilitation or "proaction" in anticipation of, and thus breaks the direct cause/effect relationship.

I agree that 'allow' means 'to permit', or 'to enable'. However, I see 'allow for' as a shortened form of 'make allowance for' (i.e., 'make provision for'), which I think holds a very different meaning to the word 'enable'.

I use 'allow for' only when referring to a possible scenario or event that merits a contingency plan...

For example:

• The expansion cavity of the furnace roof is necessary to allow for thermal expansion of the refractory lining; inadequate spacing will inevitably give rise to spalling of the bricks.
• "Did you seek to allow for that anomaly, or was it sheer luck?
• "Should we bother to allow for such an unlikely, but potentially catastrophic event?"

allow means to permit, and allow for is more like to make something possible, to enable, to make a provision for, but I'm still in doubt when I have to decide whether to use the preposition for or not.

Refining that characterizaton somewhat, consider also that the forms, "allow..." and "allow for..." are suggestive of verb (or verb and helping word) moods. To say, allow a thing most likely reflects an imperative verb mood (in the sense of a command albeit a passive and/or implied command. To allow a thing could also be indicative, a simple statement of happenstance...especially in past tense: e.g., "... you allowed the sink to overflow." (Obviously, you don't normally allow for a sink to overflow....unless, perhaps, you are installing a floor drain; but that, still would not entail indicative mood, as demonstrated next.)

Allowing for (a thing), on the other hand, explicitly connotes that the allowance more than equals the need; that there is doubt as to sufficiency of that which will or might be neeeded to be allowed. Such doubt sets the mood of the phrase, allow for, as subjunctive. (In the floor drain example, the indefinite capacity of the floor drain reveals uncertainty as to how much overflow will actually need to be accommodated...so, still, subjunctive.

So all you need to do is figure out the mood in which allow is used, then modify, or not, accordingly.

The prevailing verb moods are: indicative, imperative, subjunctive, and infinitive: moods of verbs

I believe that stylistically your instincts are correct. While omitting the "for" may be grammatical, since the verb "allow" refers to the agreement, the apposition of "cease fire" makes it sound as if that were the direct agent, not the reason the real agents used. "They" (meaning the warring parties) were the ones who did the allowing.