こんにちは　http://www.italki.com/entry/554151 The pronunciation of は・ひ・ふ・へ・ほchanged several times. 1. at the top of a word （～7th century） 波（→は）［pa］・比（→ひ）［pi］・不（→ふ）［pu］・部（→へ）［pe］・保（→ほ）［po］ （8th century ～ 16th century） は［ɸa］・ひ［ɸi］・ふ［ɸu］・へ［ɸe］・ほ［ɸo］ （17th century ～ now） は［ha］・ひ［hi］→［çi］・ ふ［ɸɯ］・へ［he］・ほ［ho］※［ɯ］is non-rounded［u］. ※ひゃ［ça］・ひゅ［çu］・ひょ［ço］、ファ［ɸa］・フィ［ɸi］・フェ［ɸe］・フォ［ɸo］ 2. except the top of a word （～7th century） 波（→は）［pa］・比（→ひ）［pi］・不（→ふ）［pu］・部（→へ）［pe］・保（→ほ）［po］ （8th century ～ 11th century） は［ɸa］・ひ［ɸi］・ふ［ɸu］・へ［ɸe］・ほ［ɸo］ （12th century ～ 16th century） は［wa］・ひ［wi］・ふ［wu］＝［u］・へ［we］・ほ［wo］ （16th ～ now） わ［wa］（い［i］・う［ɯ］・え［e］・お［o］） ※は and へ are words. But they are pronounced with the former word together. So they are treated as an exception of the top of a word. ※は・ひ・ふ・へ・ほ in traditional orthography were changed to わ・い・う・え・お according to the pronunciation after World War Ⅱ(1946). Actually わたしわ、がっこうえ are allowed for a while. But は and へ are written in words come from particles now. The reason is for easy reading. When we read わたしわきのうがっこうえいきませんでした, it's too hard to catch the meaning at once. We use は and へ（and を）as particle markers to separate the sentence to words. So we write わたしは、こんにちは、これはこれは、がっこうへ（あなたを）even now.