grammarprepositions
Can those be used interchangeably? These are three examples from the Longman dictionary. I see no essential difference between the cases so I assume you can use any option you like without any reservations (no preposition, 'at', or 'on'). Am I right?
a baby sucking at its mother’s breast
Don’t suck your thumb, dear.
a picture of Lara sucking on a lollipop
The preposition within has nothing to do with the ordinary sense of the preposition with = “accompanying, alongside, by means of, etc.”. Within means “inside” in spatial, temporal and figurative senses.
The hoard was discovered deep within the mound.
You must respond to this communication within thirty days.
They are within their rights in refusing to be interviewed.
Consequently, within is not a valid translation of German in in this context. However, English does support both German uses: you may use either with for mit or in for in.
With this option ...
In this option ...
HISTORICAL NOTE, for those who wonder why the compound with + in has this meaning:
Old English wið (cognate with German wider) originally meant “against, by, back from”, and the modern sense of with was expressed by mid (cognate with German mit). In the later part of the Old English period, however, northeast England was occupied and to some extent settled by speakers of Old Norse dialects, and over the next centuries (down into the Middle English period) many Old Norse words replaced the corresponding Old English words. For instance, they and are are of ON origin. Old Norse við, a cognate of with and wider, had approximately the sense of mid and mit, and under its influence, with shifted to the modern sense. However, the old sense lingered in established compounds such as withstand (stand against), withhold (hold from), withdraw (draw away from)—and within (against or by the inside).
When attack is a noun, the preposition on is preferred with locations, e.g.;
If attack is used as verb, no preposition is necessary. All the examples below are taken from Google news
Compare the results for attack on Israel (blue), attacked Israel (red), attack Israel (green), and attack against Israel (yellow). All four are grammatical, but the first suggests that attacks on Israel are seen as acts of aggression aimed at a specific location rather than a nation. But it is a subjective point of view, so it would be interesting to hear from other native speakers.
In the example cited by the OP, the acid was thrown (at) or poured on the woman. The woman's body is considered a surface. The preposition on is used to express physical contact with a surface.
a horrific acid attack on a pregnant woman
The main meaning of against is in "opposition to", in the following examples, against could be substituted with on.
However, between attack somebody and attack against somebody, the first preposition is usually preferred. Ngram illustrates that attacked him (blue line) is far more common than attack against him (green line)
Best Answer
The literal and most common meaning of "suck" is to draw into the mouth by contracting the muscles of the lips and mouth to make a partial vacuum. This is the definition that applies in all of your examples.
"Suck" and "suck on" are pretty much interchangeable, and in your latter 2 examples, either could work:
(although "sucking your thumb" is probably the most idiomatic in that example)
However, when it comes to a baby feeding, it is idiomatic to say "sucking at the breast", because it is as much a statement of their location and position as it is what they have in their mouth. It may even be considered an abbreviation of "suckling", which, as a verb, means to feed (a baby or young animal) from the breast or teat.
As an aside, the expression "suck at" something is also a modern colloquialism meaning that you are "bad at", or "not adept" at something.