quelque vs quel que (and quoique vs quoi que)
Summary
quelque(s) is a one-word determiner meaning "some, a few"; quel(le)(s) que is two words meaning "whatever ... may be" and takes être in the subjunctive, with quel agreeing with the subject. The parallel pair quoique/quoi que works the same way.
Explanation
quelque, written as one word, is a determiner. In the plural, quelques means "a few, some": j'ai quelques amis à Paris (I have a few friends in Paris). In the singular it marks vague quantity or identity, "some (or other)": il est parti pour quelque temps (he left for some time / a while). In a more literary register, quelque + adjective + que + subjunctive means "however": quelque riches qu'ils soient, ils ne sont pas heureux (however rich they may be, they are not happy) — here quelque is invariable, it does not agree with anything.
quel que, written as two words, is a completely different construction: it means "whatever/whoever ... may be" and is built specifically around a subjunctive form of être. Crucially, quel is an adjective here and it agrees in gender and number with the subject that follows être, not with anything before it: quelle que soit la raison (whatever the reason may be — raison is feminine singular), quels que soient vos choix (whatever your choices may be — choix is masculine plural), quelles que soient les conséquences (whatever the consequences may be).
The two are easy to keep apart with a single test: look at what immediately follows. If a subjunctive form of être follows, needing agreement with the noun that comes after it, the phrase must be quel que — two words, and quel takes the gender/number of that noun. If, instead, what follows is a plain noun (quantity/vague reference) or, in literary style, an adjective + que + subjunctive meaning "however", it is quelque — one word, and in that adverbial "however" use it never changes form.
A parallel, and often confused, pair follows the same one-word/two-word logic: quoique (one word) means "although" and is a straightforward subordinating conjunction, equivalent to bien que, taking the subjunctive: quoiqu'il soit tard, nous sortons (although it is late, we're going out). quoi que (two words) means "whatever" (as a pronoun, referring to an unspecified thing) and also takes the subjunctive: quoi que tu fasses, je te soutiendrai (whatever you do, I will support you). The same discipline applies: quoique introduces a normal concessive clause; quoi que + subjunctive is the indefinite-relative "whatever it is that".
Because these forms live in fairly formal or literary registers, learners meet them mostly in writing: official documents, essays, formal speeches. A frequent, telling error is *quelque soit la raison* — wrong, because a subjunctive of être with an adjective agreeing with the following noun is exactly the two-word, agreeing construction; it must be quelle que soit la raison.
Decision rule, restated compactly: subjunctive être immediately after, and the adjective must agree with what follows être → quel que (two words, agrees). A bare noun, or a fixed "however + adjective" reading → quelque (one word, and invariable in that adverbial sense). Same logic transposed to quoique (although, one word, ordinary conjunction) vs quoi que (whatever, two words, indefinite pronoun + subjunctive).
Examples
J'ai quelques amis à Montréal. — I have a few friends in Montreal. (quelques = determiner, "a few".)
Il a hésité pendant quelque temps avant de répondre. — He hesitated for a while before answering. (Singular quelque = vague quantity, "some (amount of) time".)
Quelle que soit la raison, il refuse d'en parler. — Whatever the reason may be, he refuses to talk about it. (quelle que + subjonctif être, agreeing with the feminine singular la raison.)
Quels que soient vos choix, nous vous soutiendrons. — Whatever your choices may be, we will support you. (quels agrees with the masculine plural subject vos choix.)
Quoiqu'il soit tard, nous allons sortir. — Although it is late, we're going to go out. (quoique (one word) = although, ordinary concessive conjunction.)
Quoi que tu fasses, je te soutiendrai. — Whatever you do, I will support you. (quoi que (two words) = whatever, indefinite pronoun + subjunctive.)
Common mistakes
Quelque soit la raison, il refuse.
Quelle que soit la raison, il refuse.
Before a subjunctive form of être meaning "whatever ... may be", French uses the two-word quel(le) que, and quel agrees with the subject that follows être: la raison is feminine singular, so quelle que soit la raison. The one-word quelque is a determiner meaning "some/a few" and never precedes être in this construction. Test: if être in the subjunctive follows and quel must agree with a noun, it is always quel que (two words).
Prerequisites
Related rules
confusablessubjunctivesyntax