What is the difference between ce and cet in French?

Both are masculine singular. Ce is the default (ce livre, ce chien). Cet is the form used before a masculine noun starting with a vowel or silent h (cet homme, cet arbre, cet hotel). It exists purely for pronunciation - ce homme would be clunky, so French inserts the t to bridge the vowels. Cet is pronounced exactly like cette, but in writing it has no e on the end.

How do you say 'this one' versus 'that one' in French?

French doesn't change the determiner. Ce livre means 'this book' or 'that book' - context decides. When you genuinely need to mark near vs far, append -ci for near and -la for far: ce livre-ci (this book here), ce livre-la (that book there). The hyphenated forms are the only way to force the near / far distinction onto the demonstrative in French, and most of the time you don't need them.

French Demonstratives

French has four demonstrative adjectives - ce, cet, cette, ces - covering "this" and "that" together. Pick the form by the noun's gender and number; the near / far distinction is optional and handled separately.

The four forms

Number	Masculine	Feminine
Singular	ce (cet before vowel)	cette
Plural	ces	ces

The plural ces is the same for both genders, the same way les and des are.

ce vs cet

Both are masculine singular. The choice is purely phonetic.

ce before a consonant: ce livre, ce chien, ce film, ce garcon
cet before a vowel or silent h: cet homme, cet arbre, cet ami, cet hotel, cet enfant

Cet and cette are pronounced identically. Only the spelling differs. If you mishear them in speech you can't tell them apart - you have to know the noun's gender.

Feminine and plural

Feminine singular always cette, regardless of the next sound:

cette femme, cette maison, cette idee, cette ecole

Plural always ces:

ces livres, ces femmes, ces enfants, ces idees

The -ci / -la near / far distinction

French doesn't bake the near / far split into the determiner. Ce livre can mean "this book" or "that book"; context decides. When you genuinely need to mark the distinction, append the suffixes -ci (here, near speaker) and -la (there, away) to the noun, with a hyphen.

ce livre-ci (this book here)
ce livre-la (that book there)
cette maison-ci (this house)
cette maison-la (that house)
ces enfants-ci ... ces enfants-la (these children ... those children)

The suffixes are common in contrasts ("this one or that one") and rare in isolation. If you only need a vague gesture, plain ce / cet / cette / ces is fine.

Worked examples

Ce film est excellent. (This film / that film is excellent.)
Cet homme parle francais. (This man speaks French.)
Cette voiture est rouge. (This car is red.)
Ces enfants sont fatigues. (These children are tired.)
Je prefere ce livre-ci a celui-la. (I prefer this book to that one.)
A cette epoque, j'habitais a Paris. (At that time, I was living in Paris.)

Common mistakes English speakers make

The big one is using ce before a vowel and writing ce homme. It has to be cet homme - the rule is mandatory, not stylistic. The second is over-using -ci and -la because the English brain wants to translate "this" and "that" word for word. Don't. Most French speakers default to plain ce / cette / ces unless the contrast is doing real work in the sentence. The third is forgetting that demonstratives don't replace the noun - "this one" is celui-ci / celle-ci, a separate set of demonstrative pronouns covered on the intermediate grammar page.