Venus and Mars across the wheel
Libra belongs to Venus and Aries to Mars, and those two planets facing each other across the chart is the oldest description of attraction in the literature. Reading the Libra and Aries opposition as a warning therefore requires ignoring most of what the tradition says about the planets involved.
What the axis genuinely describes is the negotiation between self and other: one party states a preference, the other checks it against somebody else's. That is a subject the two share rather than a defect either has.
The cardinal cross
Aries lies 180 degrees from Libra. Capricorn and Cancer lie 90 degrees away on either side. Together with Libra these are the four cardinal signs, each opening a season, and each accustomed to setting terms.
The friction that follows is procedural. Cardinal signs do not wait to be consulted, and Libra's method is consultation, so the complaint is usually about sequence: a decision arrived at before the discussion Libra considered necessary.
Hard is a technical word
A square is 90 degrees between signs sharing a mode and holding incompatible elements. The classical label is hard, meaning it produces friction and friction produces movement. Something in the arrangement gives way, and that is the aspect working as described rather than failing.
Capricorn squares Libra with Saturn's timetable and Cancer with the Moon's, so the two squares pull in opposite directions: one presses for a result, the other for a mood. Libra, wanting the room level, is caught between them.
Where difficulty is actually visible
The aspects worth checking run between personal points in two charts, not between two suns. Saturn from one chart on the other's Venus is the heavy contact for a Libra, since it puts conditions on the thing Libra reads as the point. Neptune on a personal planet leaves matters unresolved. Hard Mars contacts describe the tempo of a quarrel.
None of this is legible from birth months, and exactness decides everything: a separation within a degree behaves nothing like one seven degrees wide. The synastry calculator works from actual positions, and synastry explains what the reading weighs.
Read the combination
The Libra and Aries page treats the opposition as a pairing, with what it does well set beside what it wears down. That is a great deal more informative than a rank in a list of worst matches.
Where both birth times are known, the charts settle it. Suns supposed to clash frequently have easy Moon contacts, and easy suns frequently have nothing else in common.
Questions people ask about this
Which signs are named hard for Libra?
Aries opposite, Capricorn and Cancer square. All three are cardinal signs, as Libra is.
Is Aries a bad match for Libra?
The planets say otherwise. Venus opposite Mars is the classical description of attraction, not of incompatibility.
What makes the cardinal squares awkward?
Each sign sets its own terms without waiting, and Libra's method depends on consultation, so the dispute is usually about sequence.
What predicts genuine difficulty?
Saturn or Neptune contacts to personal planets, hard Mars aspects, and how exact the angles are.